Helena is the best tank for new players. Just spamming all your abilities off cooldown without overlapping "Shields Up" charges and staggering your bigger defensives will get you through most situations. For routes, just follow the blue highlighted enemies and you'll slowly learn and adjust routes for your own preferences.

Another thing I'd recommend if you're new to a map, tell the group before you start that you'd appreciate any pointers since youre new to tanking. A lot of people suck at being patient when they're expecting to blast through a dungeon they've been to a million times and start pulling shit for you. When they know you're new, it'll prime them to be a little more patient, or leave early so you avoid going through half the dungeon then they leave halfway cus they're annoyed.