Any tips for cutting my own hair or for a girlfriend cutting a guys hair who has no real hair-cutting experience?

Being the kind of guy i am (on a budget) I want a hair trim but I don’t feel like spending 15 bucks to get my hair just trimmed up on the sides which would take about 5 minutes if that. My hair is a medium length style right now i usually wear it down with my bangs coming about to my eyebrows but it is slightly curly and on the sides it is winging out a little bit. I just want the sides trimmed and leave the top pretty much the same.

my girlfriend said she’d trim it for me but i don’t want to look like a fool for the next month just to save 15 bucks. She has no experience in hair-cutting but claims it is a simple task.

Should I take the risk and does anyone have any other advice?