Any tips before buying an acoustic guitar?

I’m starting on a folk high school this year, and I’m gonna take a guitar class in which I’ll need an acoustic guitar. I’m thinking of starting with something fairly cheap.

So I was wondering if any of you had any tips on what to look for and what to avoid. Should I get nylon or steel? Or should i buy whatever’s cheapest and change it myself? Any specific brands I should avoid?

All tips are welcome!