With Grid, my DK's will target anyone they click on.
With Grid, my Paladin will cast something at anyone I click on, because I've set Clique to interpret Left/Right clicks as heals; the only click on a Grid frame that Clique interprets as target and not cast is Control Left Click.
But you can configure it however you like.
It is Clique and not Grid, that is preventing you from selecting targets with Grid.

As per Mosg2 in the DK Manifesto, I'm trying to use straight clicks.
I was using Alt + Left, Alt + Right, Ctrl + Left, Ctrl + Right, etc.
He was using Left, Right, Scroll Up, Scroll Down, Middle, Thumb 1, Etc.
Much easier to heal without mod keys, with the mouse.

If you don't have the two minute trinket, that will be #1 priority.
After that two pieces of gear for the +300 Resilience bonus, with a possible emphasis on Helm (Meta Gem) and/or Gloves (extra bonus, if its useful).

Two of the remaining five pieces, for the four-piece bonus might be good.
Especially if they have sockets which you need to activate your Meta gem.
But I would also consider going +Res pieces in slots where you have no Resilience.

Until 4.1, stacking Resilience is probably the best you can do, in pvp.
After 4.1, resilience calculation changes such that over 32.5% (just over 3k Res) has less mitigation for the same amount of Resilience.

You could ask for a Blacksmith with all recipes to link you, in trade.
Or possibly search wowhead.

#show
/cast [mounted] !Crusader Aura; !Concentration Aura