For me side projects have been things I'll make to do something that others will use. Some people call it innovation, some call it side business. But that's how i look at side projects. So the points below are more to do with entrepreneurial experiences.

1. If there are more people involved, ensure that there is work for everybody (also level of commitment is tested by how much they put in). Also have as varied set of skills as possible. So that areas are well defined in terms of scope of work and areas of expertise.
2. Put in some money. Money is super glue. It will ensure that you're committed to the thing. Things change when decent amount of money is involved. You're invested, as may be others.
3. Learn something as an intention. This has nothing to do with the learnings you'll get on the way. This one seems obvious, but nevertheless needs to be said.
4. Set timelines and deadlines. Ask someone else to check on whether you're keeping on to your deadlines or not.
5. Don't go live without proper testing.
6. Make something you feel strongly about. The path will be exciting and clear.
7. Talk to people to get their feedback on everything. You may not like what's told to you. Listen dispassionately. Absorb everything. Feel miserable. But listen and think about it after sleeping over it.
8. Continuation of above point. Talk to varied set of people in terms of backgrounds. You would be surprised as to how differently people think.
9. Ask for help when stuck. Kill your ego and be vulnerable.
10. Check out what's already available. What value are you adding. And make it!