There are lots of right ways to prepare a team for the GEM Tournament, but here are some suggestions to get you started.
Get interested girls together once every one or two weeks to train together. Training in a group tends to be more fun and fruitful than training alone.
Each week, in addition to working on a past contest/tournament problem set for your division, introduce a problem-solving strategy or nugget of math content that may help with a problem in your practice set or in the future.
Include a practice hands-on challenge once or twice per season or as often as you like.
Keep it fun and remind girls that getting even one question right is to be celebrated. The problems are designed to be very challenging for all the target grades. If training more than 4 or 5 girls at a time, keep practice team sizes small (2-4 per team) and change up team formations frequently until a few weeks before the tournament, if practical. By that point, it may be helpful for girls to start practicing in the teams they will compete in at the Tournament.
Save time at the end of each meeting to review a particularly challenging problem or have the girls share what worked well or what they'd like to do differently next time.
This document provides more guidance about possible GEM Teams curriculum and other suggested resources for coaching.