Just ask yourself these questions;

1. Do I have aggro on enemies/boss?

2. Is the healer able to keep my hp from falling too fast?

3. Are you constantly tab selecting through enemies to maintain the said aggro?

If you had said yes to all of these questions then you are already doing a good job in tanking. Whether it be 2 mobs or 8+ mobs as long as you've got hate and holding it while managing your defensive cool downs you're doing things right. Also, switching between enemies to check aggro tables is what separates the OP/Flash/Unleash spammers from the real pro tanks. Combo splitting is something you will need to master to better manage your tp or mp.