Don't read this checklist without practice, you will blank in the competition (of course you will forget what you read) because the time-clock is running and you don't have time to read this again during competition. The best practice is read and applied at the same time.
Read a lot of write-ups and of course practice the challenge!
Do many challenges as much as you can. Online practice site can refer here.
CTF is great for industry. Trust me. It worth for your future for every seconds you spend to learn.
Split your task during competition. Don't try to be "hero" or be "I'm the genius one in my team". You should learn to know your limit. Not everyone can master every categories in CTF. Example, there is a RE guy, Pentest guy, and Scripter guy in one team.
Do not study hard a day before CTF, sometimes when your brain is loaded up too much.. you will blank during the game. Just relax and calm.
Final, don't show off your skills. There is a lot of pro out there. "Showing off is the fool's idea of glory." - Bruce Lee