Tuition

I already replied to you on the other thread - and also received the same as PM. Please refrain from posting almost same messages all over the forum - once in the right place is enough!
The other post I replied to was about tuition, which is not a likely field of work for foreigners, due to formal issues (see my reply).
So here I will write about becoming a school teacher.
To become teacher in Singapore, you need a recognised educational university degree (and applicable teaching experience). For recognition of your foreign degree and jobs at public schools, contact the Ministry of Education (MoE). For jobs at private schools, you need to apply at the schools individually.
Depending on the subjects you can teach (English is not an option for non-native speakers!), there is more or less demand. However, you will always be at a disadvantage compared to local applicants, thus you must be better than them to get the job.
It is usually a good idea to be in Singapore during the job search, as you won't be considered or invited for interviews if you are not. You can then return home while waiting for the work visa approval process to complete (this takes longer than a month in most cases).