Howdy-ho, Stillwater!

The best shield-use spec is the Blue tree, The Defender of the Free

I mainly play Guardian as a Blue Tank, since I struggle to make him work as anything but:

Here's the guide I've been using - https://lotrohq.com/blue-guardian/

The only relevant parts of it for you at level 49 are Virtues and Trait Points

I hope it helps!