A photo might help people diagnose. Sometimes, though, it doesn't matter what you do, if it's on the downhill slide.
Personally, I would trim it very gently (not trying to get to fresh wood, because if it is ill it can't fight off diseases introduced into a fresh cut) and put it in morning sun/afternoon shade. It does need sun to warm its roots and encourage budding. Remove only the dead leaves and let it go.
Water until you are sure that the root ball is wet, then don't water again until the soil is just damp under the surface. Your biggest risk at this point is wet roots that can rot.
You could give it a very gentle fertilizer, something with low npk. It isn't going to hurt. The tree will take up what it can use.
If the tree continues to grow, your problem is going to be dryness. As it is here in California, maples don't like dry summers. You get leaf cell collapse when the tree is unable to provide enough moisture for transpiration through the delicate leaf cells. There's a reason that no one is growing maples there!
I'm hoping to install a misting system in my shade cloth area before summer gets too hot... but that's quite an expense for one little maple. And once or twice a day misting probably isn't enough to prevent some leaf burn. Maples do survive leaf burn, but they are probably weakened by it. Some people around here defoliate in mid-May or so, and encourage a new flush of growth that develops during hotter weather, with the theory that the leaves grown in May and June are stronger than those grown in March. Other people feed the tree with a silicone based agent that is supposed to encourage stronger leaf cells as it is taken up into the tree's system.
Hope this helps. Remember, if you have a sick patient, you don't give them tattoos and poke around on them too much. Let the little tree grow first. Dead branches (unless they are diseased and the rot is moving inward, which would look black instead of brown) don't hurt anything and can always be taken off later.
Joanie