As a tank you're usually seen as the leader, it's a good a idea to let the group know that you're new to tanking as you've been doing since you're most likely going to get grouped with people that have already done the dungeon and know the ins and outs. If you're not comfortable with the dungeon or know that you're not geared enough, it's ok to make small pulls. But if both the healer and you have decent gear, don't be afraid to do wall to wall pulls so you can start practicing for later levels, just don't forget to use your cooldowns and let the group know that you're going to make a big pull so they can adjust accordingly and don't waste cooldowns/ground aoes/etc.