It really depends what you're playing against how to use his avatar. Against a crew with lots of Companion effects, you want to keep him back, or only bring him out when there's no danger of more than 2 models attacking him (I think that 3 minions can take him down barring soulstone use). Against a "normal" crew, unless you put him in range of a heavy hitter that can kill him in one activation, Som'er can take one, maybe two rounds of attacks between HTW and Armor, and then you can pull him back with one of your support models, meaning you can use him as a attacker.
As for attacking, I find charging in, triggering "Atta Girl" once or twice, then using Reckless to cast Swamp Gas is pretty effective.