You need more than a few tweaks, I think. The problem is you don’t have much damage. You need to at least triple your damage.
What are your OA and DA? Your DA is probably good but I’m guessing your OA is too low. You want your OA higher than your DA.
You should pick one attack and make it as effective as possible.
The damage from Blitz scales off your shield damage. So it’s not great as a primary offensive skill. It works best to just put 1/1 in it. You’ll wind up with 5/5 or 6/6 once skills from items are takin into account. That makes it useful.
Blade Arc works pretty well. You want to try to maximize physical and internal trauma damage. Try going 1/1/12 on the Cadence Line along with your maxed Blade Arc. Deadly Momentum adds a lot of damage to Blade Arc. (Look at the orange text in the tooltip.) Going Clean Sweep is an option that you may or may not like. (You use Cadence until Blade Arc comes off cooldown, making sure DM is up each time you use BA.)
Next question is what are you trying to do with your shield?
If you are going with a block build, why do you not have Overguard? It’s the “make me immortal” button for shield builds. And max Shield Training. You want to as much block recovery as possible. You can get 85% trivially. You get 20% from Shield Training, 20% from Serrated Shell, and 15% from Shieldmaiden. Overguard gives you the other 45% percent. It’s pretty easy to get your block chance above 70% (the vendor in Devil’s Crossing sells a potion that gives you 10% for a short time). If you have 70/100 block/recovery you just take no damage from anything. You can get more recovery by taking Overguard and Shield Training over the max with items, so you can even drop Shieldmaiden.
Next thing is War Cry. Break Morale is awesone. Physical resist reduction and skill disruption. The resist reduction will increase both your physical and internal trauma damage considerably. And you get the skill on Assassin’s Blade for the same reason.
The skills on Targo and Obelisk aren’t helping you.
You could try some combination of Oleron, Anvil, Dire Bear, and Bull. Rhowan’s Scepter gives health, defense, and damage - though you may not be able to afford to take it. Empty Throne and Wolverine are useful and also the most efficient path to get to Oleron.
You also may want to go for one of the big health regen devotions. Either Giant’s Blood or Healing Rain. (Unfortunately you can’t get both Tree of Life and Oleron. However, you can do Behemoth and Oleron.)
You also could invest more in Nightblade. Veil of Shadow is good (the OA reduction). Anatomy of Murder gives you OA and damage. Blade Barrier is a good 1 pt “get me out of trouble” skill.
Markovian’s/Zolhan’s aren’t that useful for a Blade Arc build since Blade Arc doesn’t proc them.
Short advice: Take points out of Blitz and max Overguard and Shield Training. Completely respec your devotions and go for offensive procs. (It’s not going to help immediately because you’ll have to level them up.) You may need to do this several times until you get what you like. You can farm Crystals at Ultimate Lower Crossing.
I hope some of that is helpful.