From the EXTREMELY limited knowledge I have (I have tanked in WoW, but not really in LotRO), you'll want to "tab-target" and use Precise Blow, especially with only a handful of foes. For big packs you want to use War Cry, maybe Goad (I've heard either "Goad is useful, use it" or "Goad is worthless, forget it"), still tab around and Precise Blow, Maddening Strike is helpful too.
From what I understand Wardens are difficult to tank with at lower levels and you really have to rely on people single-target firing down whatever you're attacking; they'll pull threat really easily if they just randomly target or AOE things. I ran a GB on my Hunter with a Warden as the MT and found if I used Rain of Arrows I would pull, but if I just hit the "assist" button to make sure I was targeting his target and used single-target attacks, he was okay.
Also, if low level instances are anything like WoW's it's not a huge deal if you lose aggro to a DPS, because you just don't have enough tools to hold aggro against everything. Obviously you should try, but we have a saying in WoW:
If the tank dies, it's the Healer's fault
If the healer dies, it's the Tank's fault
If the DPS die, it's their own fault
Focus on keeping aggro off your healer, but if DPS are trigger-happy and pull threat because they can't assist the tank, they should be facing the consequences.