Looking for a job

As you are probably aware if you did some online reading, Singapore admits foreigners to work only in areas where there is a lack of appropriately skilled locals. (In fact, any employer must show that they couldn't find a suitable local before they can hire you.)
There is no shortage of accountants in Singapore, and good schools constantly churning out more. Thus, unless you have specific niche skills that make you valuable, accountancy is not a field giving you good chances.
I am not familiar with fitness coaching and whether skilled trainers are sought after. You'd have to do your own research to find out, e.g. by contacting companies in the fitness industry.
In general, anything less than three years work experience in the particular field makes it difficult to get a work visa. How long did you work as fitness instructor and what are your paper credentials (degree, certificate, or similar)?

Thanks for the infos,i appreciate your time
Am a ex footballer in thailand,in 2015 i joined   Herbalife as wellness coach.but
Am more into fitness and i do follow up with the healthy nutrition. Presently am working for Cameroon  telecommunications regulatory  board as a personnel to the main accountant from our ministry of finance here in Cameroon.in December getting married to my Singaporean fiancée,so I will be moving from here.

As spouse of a Singapore citizen (who has sufficient financial reserves to pay for your living expenses - this usually means S$5000/month or property ownership), you can get an LTVP (Long Term Visit Pass) and move to Singapore. However, you cannot work!
If you want to work, you must apply for a work visa (WP, S-Pass, EP) like any other foreigner and the same conditions apply (which I outlined above).
After living in Singapore with your spouse for a year, you can upgrade to an LTVP+, which allows you to work on LoC (Letter of Consent) - the thresholds for this are somewhat lower than an EP or S-Pass, but getting one is by no means guaranteed.
Herbalife and similar sales experience will not help you more than accountancy. Singapore football teams are very bad and might value foreign additions who are better - but I have no idea if they can pay for it.

I understand everything you are explaining
Actually financially am doing okay,I move because I want to be with my fiancée.sure I will apply for a working visa as you said above and hoping to have a job. for what I understood and was told ,I need to be paying my taxes and if as a foreigner I wanted to get a residence permit , i will need to own a business?But I haven't still understood how their tax policy works,for workers and non workers? If I could be paying it even if am not working in singapore,just traveling to other countries doing my fitcamps as I do recently?
Just avoiding the ignorance and getting into probs

There are separate (residence) visa for employees (WP, S-Pass, EP) and self-employed (EntrePass). The latter is very difficult to get, but it might be easier if your spouse owns the business and employs you - ask a incorporation service provider like Hawksford or Rikvin for advice if you want to try this.
After becoming PR (Permanent Resident), which usually requires 3 years of living here with your spouse, you can start almost any business without restrictions - but I guess you don't want to wait that long.
Tax on earned income is paid by yourself after the end of the year and rates are fairly low (see www.iras.gov.sg). For business taxes you need to consult an experienced accountant, as the rules are complex.
Freelance work in other countries (as what you are planning) is VERY difficult to do in a legal way - and you run the risk of having to pay tax both in the host country and Singapore. Some people do this "under the radar" by travelling on tourist visa and never declaring any income, but this is of course illegal and not to be recommended.

Thanks for your time
I'll keep everything legal and try to get a job after mariage.as well starting up from  there
If an advice I will surely contact you
You live in singapore at the moment ?

Why not engage a job recruitment agency in Singapore who specialise in helping foreigner to look for a job? They will be able to advise not only on jobs but also on the process / paper work on how to apply a job in Singapore.