I don't like side jobs because you are still going to work under someone, I won't expect anything great or life changing from this, it will be good if you can learn a skill that's not going away any time soon, a skill that will last you for a very long term, for example, I.T specialist.
Your life starts changing the moment money starts flowing into your bank account from different sources of income, a good side job or business can be very handy for a grown up man.
It is still depends on the someone preference because not all can start small business as there are no capital and difficult to run it without any knowledge but it is really best because it would be passive income in the future if your business will be successful but for now if you have like family to feed and if you take risk to start a business and then it wont be successful both of you and your family are at risk.