Can you hold steady with a kids bow? If so, try shooting lighter draw weight bows. Also, are you getting shaky after shooting a number of arrows or are you shaky on the first handful of shots, too? I'd try to eliminate strength/stamina from the equation (the simplest explanation) before trying anything else.
For me, aiming is secondary. As my groups open up, I usually find that I'm focused on aiming, not the other fundamentals. None of my gaps are going to matter if I'm out of alignment, if the string whacks my nose or armguard or if I'm so focused on aiming that I create side movements that throw off the arrow before it has a chance to leave the string. I've seen older guys wobbling on 35# target bows still manage to put decent shots on target because, I assume, the other fundamentals are there.
After that, I'd take a look at breathing. This helps strength but also helps steady your hold since you are steadier at some parts of your breath cycle than at others. I'll let others chime in on what is best here.