Best season to move to Spain

What is the best season/time of the year to move to Spain, and why?
I suppose that depends on where in Spain. But any where during the summer can be a pain. Offices close early, fiestas can mean a city, town, village can be shut for days.

How do rent prices fluctuate based on the different seasons?
Not that I have noticed in inland Galicia. But I would have thought in Summer coastal areas would have a greater demand thus lowering the chances of finding a longer term rent.

Is there a change in the job market depending on the seasons, such as job availability?
I do not know but in reading/watching the news it is said that the hospitality trade obviously takes on more staff for a short while.

Are there any seasonal festivals or cultural events that would allow you to learn about the country?
All festivals/events teach you something about the country you live in.

What are the times of year to avoid for expatriation to Spain?
Summer read the answer above.

During which season did you move? How did it go?
Winter but during a lovely sunny period so things stayed dry. Horrible company damaged several items, they were insured but that was not answer as you why they did not pack correctly. Customs up held our household goods even though we was coming from another EU land. We also warned that a large lorry could not get to the house because of the narrow and steep road. Took a video of the road. The message was not passed to the Spanish contactor.

The tourist season is commonly June, July and August in Spain. Until mid September prices of housing will be ridiculous and inventory will be low to non-existent. In major cities one can add student activity to that. So move mid September or later but not much later. Landlords here tend to think short term, so it is of no use planning long term in Spain. Beginning of September they will start getting nervous about new renters, especially if they see more inventory appearing, so more competition.
So that is the best time to start looking. Do not wait too long though or the inventory will dry up again or it will simply be taken off the market by owners getting tired of seeing prospective renters and who already made lots of money in the usual summer months and do not really need the annual income.
In coastal areas this is especially a dominant symptom, since there at least 80% of homes is occupied by outsiders.
Also take into account a very unusual aspect of the housing market that is typical for Spain and maybe a little for Portiugal as well. Many baby boomers have inherited homes they do not need and will not do any or barely maintenance on and that also do not suit their needs as they have bad locations for them (not in or near major city) ancient lay out, built for large families which do not exist anymore, constructed poorly etc). This is why there is a huge inventory of 1 million empty unused homes in Spain  n top of that comes the emotionalism of many Spaniards that they heavily overvalue the value of their homes, so ask way too high a purchase price (often 2-3 times its real value) or rental price. Many will not budge on that until they get financially in trouble with teh house or never, so they let thr house decay. rental protection has dimineshed in favor of owners but it is still ridiculously costly (at least EUR 700 and a many months of wait time for a court decision which can get worse if courts are on strike for months like now in Galicia.
The realty industry, so the brokers are not regulated, which is good, but it also lead here to  often poor quality of service because of ignorance and poor sales skills. realtors and brokers are mostly not qualified to help you with a rental (or sale or purchase) as they like to only provide services for overpriced A1 location objects, not affordable stuff. So look for direct dealing with the owner instead.
This means you really need to be well versed in Spanish and in the quirks of the rental market. In my opinion there is a huge market for brokers who offer a service for a fee here but those do not exist in most places.
One matter that I caution you about is the deposit. Insist on having the contract and deposit registered with the local authorities and do not pay more than 1 month as that is all those will cover. It has as a consequence that they can come after you for the renters tax they now started charging, but they may not. Of course, if your have no contract registered there is usually no such tax. see it as an insurance though.
Never accept any deals where more than 1 month deposit is required. It is a set up for trouble. Never also sign any deal unless all is fixed that needs fixing as the landlord will disappear and not fix most things once the contract is signed. If he promised to put in a furnace, insist it gets put in first before you sign and move in. Otherwise it is just a trick to have you finance what he cannot afford. You're not a bank though and you would be running all the risk.
If an owner lives very far away from your rental, do not sign. That is a set up for no services at all with issues with the house, no fixes. Do not believe in any stories of the landlord 'having someone to take care of things'.
As to jobs, there are no jobs for foreigners in Spain beyond seasonally teaching English and that often at ridiculously low hourly rates. Here in Spain a language teacher with a university degree tutoring privately will often not charge more than EUR 6-8 an hour! At bets you can earn EUR 10 teaching a whole class and it won't be regular large volume work. It is no surprise that most Spanish kids are leaving the country and leaving it mainly to pensioners. That is a demographic trend.
All you could try is service foreign pensioners here, but then you would need to go live in areas where they abound. That may be a growing market. Take into account though that the Spanish are getting more and more difficult for foreigners, especially taxing them and demanding more paper work, so many pensioners have already left. The foreign wealthy are now also being chased away, while they are far more welcome across the border in Portugal.
Setting up a business here is also only for the very happy few who are so foolish.
This is mainly a place for old pensioners like me,
Festivals abound in summer and late spring, even autumn, but in many areas it is largely for the young. Only in very touristy areas it will still have the Spanish flavor instead of loud modern music and loud fireworks.
In Galicia I would recommend then especially fish related festivals where one can inexpensively taste the local fish. The music is not great there though. In Andalucia one will find ten times better but that is no wonder with so many foreign tourists there and a far better financial situation of its inhabitants.
The richer the towns and cities, the better celebrations.
Of course the real flavor is not just in festivals and fiestas. One can find it in local bars and restaurants mainly frequented by Spaniards not tourists or on beaches mainly Spanish visit. The thing is that the younger generation is not very 'Spanish' anymore.
Of course there is no denying that the siesta and Sunday shop closures are typically Spanish.  ;-)
Your bets bet is in talking to neighbors, shopkeepers, drivers etc.. They are Spain and often love talking A LOT! Especially in more rural areas where people take their time and little is urgent. Be prepared that politics and religion are hot and main issues on all levels.

Very useful questions that I am interested in the answers to also.. we are moving to Barcelona this year, probably second half of September.

And we're looking for an apartment if there are any landlords/opportunities/further advice - it is much appreciated.

This is a fantastic way of putting it!

Key ingredient stated on this post: Try to negotiate directly w/ owners.

I found my flat three years ago, on foot. I live in Madrid and I spent nearly one month looking around for a decent flat to move in. I live in a decent area - Prosperidad - and I have tought about moving into another larger flat and what you mentioned is 100% accurate some of these flats are beyond repair - literally shitholes (or what is known here as pocilgas). Even when dealing directly w/ owners, be careful because if they get a chance to screw you - they will. You will hear a lot of BS about boosting economy and so on which is plain and simple horse crap. As a matter of fact, a few months ago there was a property hike in Madrid, and people in my neighborhood went crazy racking up rental prices - and guess what? They're not renting!

Before moving in into any apartment/flat DO an inventory and check the conditions of such!!!! Water heater, toilet hoses, etc... On the other hand, check what kind of neighbors you have on both sides, above and below cuz you could run into some (serious) issues. If you find Caribbeans, Northern Africans and in some cases, South Americans try to look for something else. I live in a building w/ some elder and it's just fine.

Some landlords like to be paid in cash and this is something I declined due to tax filling purposes.

Also bear in mind utilities. For all you will need to have a Residence Card and Bank Acct. No company will provide services w/ just a passport.

Paperdetective.   

Quote

Then are Spain and often love talking A Lot ‘

And maybe they are not alone !

Anyone considering moving to Menorca should first of all spend a couple of weeks here in the winter.  Menorca is a wonderful island but the winters can be tough.  There's seldom any frost and only occasionally a little dusting of snow, but because the island is small and narrow with no range of mountains to protect it, it is prone to very high humidity and very strong wintery winds.  A salty dampness can be pervasive and fungus spores just love it , giving everything made of leather a grey fuzz.

The houses are built with hot weather in mind with little attention to insulating against the cold and damp.  Central heating is a rarity and electricity bills and loads of logs can be crippling.

Once the tourist season is over, much of the island closes down.  The two primary cities of Mahon and Ciutadella remain open and of course there are various fiestas but life during the winter can be a trifle dull. 

Any seasonal work is brief and there's precious little to be found from October to May for the native residents so outsiders are very unlikely to find paid work. 

So, if you have a bob or two and can afford to live in a centrally heated house close to a town center and have sufficient cash to see you through the winter without working, your cup runneth over!

The islands are great option but a bit expensive. If budget is not a problem... I really don't know which ones are better, if Canarias or Baleares... I believe Canarias are far cheaper than Baleares...

Yes, the Balearic Islands are certainly the most expensive parts of Spain and Menorca in particular.  However, it is claimed that Menorca is also one of the safest parts.