I currently have a GMPC that's a liberation champion. In combat, I do my best to do as little damage as possible, so that my squishy family can do all the heroic stuff.
We're currently level 2, for what it's worth.
I usually open combat by trying to position myself between the enemies and the players. I then try to intimidate whoever is closest to the party, then raise a shield.
Once the enemy has engaged the party (by which I mean my champion, 9 times out of 10), I do a lot of grappling, tripping, and shield raising, which are all great 3rd actions for STR based characters (or shield wielders, in the case of Raise Shield, not that I can convince my Druid stepson of this). If enemies get too close to the party, I'll also start trying to Shove them, or using Reposition.
Also, Lay on Hands is a 1 action focus spell, so that gets busted out for a 3rd action when necessary.