If your still learning the fundamentals of tanking then stay within your comfort zone.
The best advice I can give is to learn the the layout of the instances, the route from boss to boss, where mobs are located.
Since your a DRK maybe make a macro for Living dead.
This could give you and the healer a good amount of low risk up-time while letting the healer know they need to not heal you for the 1st 10 seconds and heal your max hp within the next 10 seconds
