I think, you should start out with a larger company, which has a team with at least one senior dev.
Usually, startups need to move fast and consist of hype-driven young people, often without too much experience. However, in the first years, you should take it slow and careful, learn the basics and learn them good. You should get to know what is important and how certain things can be done and what effects they have. To put it into a nutshell: you should have mentors how show you the ropes.
When I finished my studies, I was ready to change stuff and I was the first developer of my kind in the whole department. I knew lots of things and many things better than my colleagues. However, I failed hard at many things, because I could not get the necessary guidance to slow the F down.