I think by now you should have read this post about a tutor who earns $10k a month. Most of what is mentioned in the article is quite true and I can vouch for its accuracy. Some comments on it though, before you quit your job to become one:
1. There's no CPF contribution by employer, leave, benefits, company dinners, health insurance sponsored by company. There's no company benefits at all.
You must learn to take care of your own affairs. Being a tutor is not just about the teaching part. You have to learn to manage your own affairs, save up for your own retirement and do your own accounts and tax. If you really hate these kind of admin stuff and do not want to pick up stuff like accounting, investment, insurance and a million other things that normally people take for granted, then you should seriously consider ......