how would you rehab a weak arm, where would you start?

My right side as always been stronger and since it's easier to get things done with that arm I'm sure I've neglected my left arm. But I still see a lot of potential there. My left hand has no grasp, that is the least of my worries so I wouldn't start there. My bicep works but is weak and limited range of motion. My tricep has a trace, I have to believe if I can make it fire that it can be strengthened. I can pull my elbow / arm back, rowing motion, but pushing it forward it only goes a short distance. If I try to pick my arm straight up using the shoulder it goes a little but not much. My wrist can turn out, I can get it back in but mostly with a flip. I can shoulder shrug pretty strong but my shoulder blade feels kinda locked up. With all of this I know my arm can be better and do more for me, but where do I start? If you were to prioritize, what area would be the best to start with, and then? I appreciate the help on this, thank you.