Thinking over offense from side control ...
I like the idea of attacking the far arm. If his hand/arm is on my headside, then my main arm attack needs to be a keylock. If his hand/arm is on his legside, then my main arm attack needs to be an armbar.
With the keylock, I want to use my headside hand to grab his wrist, with my elbow in his neck or shoulder. That keeps him from bringing his hand behind his head--which is a very effective defense against the keylock.
The headside hand is the post. That is how I keep both the L-shaped bent arm and the space between his wrist and shoulder.
I also want to simultaneously use my legside hand to pin his elbow against his body. I can just squeeze his arm against his body or grab the sleeve. But I want to trap this elbow against his body to further isolate the wrist I am attacking.
From there, force the arm down with the headside hand, and slide the legside hand along his arm until I can slip it under his arm at the elbow, clamp my wrist and lock in the keylock.
I might have to wedge my arm a bit to get it under the elbow, and to get the elbow increasingly flared out. But if I just take my time, I'll either get that or the choke.
Maintain a neutral side control and crank the lock. Be wary of being pulled over to the lock side in a sweep. Depending on how he reacts, you might even be able to jump to mount and finish off the key lock from the mount.
Always be ready to give up a mediocre keylock attempt for a shot at an excellent choke opportunity. If he's fully committed to defending against the keylock, then he might be unbelievably susceptible to a choke. I'd bring the headside, wrist-grabbing hand back to grip the near collar (pulling across his body toward you) while using the legside hand underneath to grab the opposite collar (pulled away from you).
