The easiest way is to run your side business as a sole proprietorship company. You only will need to get a AHV number [1]. To get this number you have to prove

The easiest way is to run your side business as a sole proprietorship company. You only will need to get a AHV number [1]. To get this number you have to prove the AHV that you are not fictitiously self-employed [2]. This will require invoices from at three (or more of course) different customers. A recurring payment like eg. from an Adsense account should be sufficient also. If you have this number you can fill out your tax formulas and conduct all expenses of your side business [3]. [1] If you have a work visa you already should have a AHV number. [2] If you would work as a "freelancer" for only one customer it will look like your "employer" just want to avoid to pay into the social system. [3] Your sole proprietorship company should be profitable after about 5 years.