My advice to the OP is to list builds you've tried and struggled with because we can certainly help you. There's already a lot of good advice in this thread. Some of your struggles might be gear oriented or playstyle oriented. I've been playing an Offensive oriented Templar since launch and she's my most played class at 140 completed ops (going for the banner). While I was still hashing out gear, I ran this build.
This is what it looks like at lvl 8 (when I switch from Routine to Threatening)
Strategy: You excel as a spawn Nuker even with a low common one-handed. This is when you'll develop game knowledge for things like knowing when to Shield Wall enemy attacks as PARRIES, knowing how to spawn dive to pop off your WoH/SP combo burst DPS, learn how to facetank the Demmon Commander / Venatori Commander and kite the Red Templar Commander.
This is what it looks like at lvl 13 (should be on Threatening at 8+)
Strategy: You're building towards extra Guard generation in Unbowed and your only access to temporary invulnerability in Unyielding. Then its back over to the first tree for some important passives. You'll eventually discover that Shield Wall parrying is plenty of Guard generation and that Unbowed can be swapped out for something else (Like Horn of Valor, Line in the Sand, Bodyguard, Challenge, or Payback Strike).
Anyhow hope this helps. Templar is a powerful hybrid character and can function well in multiple team setups.