Bear in mind that since I havn't seen you play or any logs, this is just a number of suggestions of top of my head:
1. Make sure you're in defensive stand! I know I've often forgot...
2. Pop dps-cooldowns at the pull to get a nice amount of threat right away. Since dps players like to burst at the pull and since your vengeance will be low or nought, this really is the critical moment!
3. Try to get some more hit/expertise. If you miss a lot you wont get any threat

I havn't tanked on a warrior in ages, so I have actually no idea if going for the cap is advisable. I just figured that since it works for the Bears it might work for a warrior too. You might want to check the guide on that one...
4. Be patient and get better gear. Since you're (probably) just doing HC, don't worry too much about it. You might get a PUG with monster dps'es that totaly outgear you. It can be hard for anybody