Well, I haven't seen you comm more than a few times, but I am also a fellow comm failure, so I'll tell you what I tend to do wrong:
1) Not paying attention to Marines. They die without meds or ammo, and every second counts, be it a med or a phase gate.
2) Not keeping track of RTs. Can't win without them.
3) Not keeping track of the hives. Newborn scans them a lot. That is generally a good idea.
4) Forgetting to upgrade. Marines will die without armor or weapon upgrades. HMGs are necessary.
5) Forgetting to give out guns when you need it.
6) Not keeping your general plan in mind. Shooting for a two-hive lockdown? Make sure you get phases up, turrets up, and WATCH the phase gates. Just rushing? Make sure you remember to send people out to get phase gates up.
7) Not giving Marines orders. Generally, Marines should know what to do in specific cases, but you HAVE to let them know what the next plan of attack is, or the team will lose.