Left arm = zombie arm

[freelans]

My left arm (I'm right handed) looks absolutely dead when I hit.
Watching some vids of myself, I notice that my left arm goes down and in on forehands instead up up and away.
On backhands (one handed) I forget to spread my left arm back.

I know I need to remember to do this but when I'm focused on the ball I fail to do so.

Any tips on how to ingrain proper left arm motion?

Thanks.