We've been in Valencia since September/October, so are in no way experts. But, a couple of things stand out in particular:
Number One. The Fallas. This is the most amazing fiesta I have ever seen, in the world, and no matter where you are in Spain, you have to see it. I could wax lyrical for hours, but words cannot express how amazing it is. Read up on it, watch YouTube videos, but whatever you see, it is a thousand times better in real life. If you are travelling from afar, you will need to book accommodation at least six months in advance, as in addition to the Valencians, I think half of Madrid travels to watch too. Not sure of exact dates, but around mid Feb I think.
Number Two;. The Santa Semana processions at Easter. Now, we are moving to Southern Spain in a few weeks, and apparently there are truly magnificent ones there ...but if you want to go small scale and intimate, but incredibly moving, up close and personal, then try a trip to Terruel and get to the Plaza del Torro. It's a small square, so get there early evening, and bag a spot at one of the restaurants under the arches around the edge. We watched the processions into the square, and then once every one was in position, silence fell and you could have heard a pin drop, above us from a balcony, two acoustic guitars started playing, then a soloist sang beautifully. More guitar, and two dancers in traditional dress swirled and danced like wraiths. Sometimes small is better, and although I'm not of a religious persuasion, the atmosphere and the magic of being up and close brought a tear or two.
Just a couple of other nice simple things to do if you're in Valencia province. Take a trip to Albarracin, up in the hills, a stunningly beautiful Moorish town built in red stone, picture postcard perfect, interesting cathedral, stunning.
If you like walking, then a couple of nice ones. The mountain gorge of Chulilla (if you're into climbing, even better, there were teams from Germany, Scandinavia, France while we were there.
Nice and simple, Pedralba has a lovely little restaurant serving delicious food, and then go for a walk along the river, where you can swim, picnic, see a variety of wildlife. Unsignposted, so a secret and wonderful find, lots of bird life for any budding ornithologists!. Ask for the Sports centre.
Also a another river walk between Buñol and Alborache, following the route of the old mills. Quiet, and peaceful, and then have fantastic meal from Menu del Dia at either El Forcat or Abetos, we haven't found better food anywhere in the province.