Forum Moderators: LifeinAsia
If the former, then the best thing to do is go freelance/self employed. As far as I'm aware you don't really need to even think about setting up a 'company' or T/A (Trading As) unless your income is VAT-able.
In the latter case, declaring the additional income would be best in theory. However, the most obvious advice is actually the best - go see an accountant before you go further.
Usual disclaimer applies - I am not an accountant nor business adviser. Please seek proper advice before proceeding - it will save you an awful lot of trouble when you have to do your tax returns..;-)
Syzygy