Dekans
In Rohan, if you are one of the only two classes that can get mobs to hit you instead of someone else unconditionally. If you are low on vit or none at all, inform the party of your inability to tank, but if you're at least 3/1 whatever/vit with up-to-date armor, you should be able to tank for a little while. Work with your healer and see. Use AoEs to attract adds the mobs around the main one; you can make it work like a low powered taunt. If you are not the main tank, always be on the lookout to get mobs off your fellow mages, healers, archers and dhans. If you notice someone's health is plummeting fast, Heal your teammates.
Dhans
Don't attack first ever as you are squishy. And don't pull without sprint on. You will remember that your archer buddy and share with him you are Dex buff, he'll be grateful. And you have a couple of limited forms of Crowd Control use them if the situation gets too bad. We provide you Rohan Gold at low price, order form us any time.
Knights
Even if you're not a tank build, keep a shield handy, you can tank decently well even if you are not a 4 vit build. Use bleed on other targets than the main one to keep some limited aggro on them. Always be aware of what's happening around you and taunt stuff of the weak characters (Rohan online Gold).