While dragging layers around is often a valid option, it's not the fastest way to put a layer at the top of an 80 “layer composition, especially if it's near the bottom. There are several keyboard shortcuts that will come in handy.
To bring a layer to the front, press Cmd+Shift+] (Ctrl+Shift+]).
To bring a layer to the back, press Cmd+Shift+[ (Ctrl+Shift+[).
To move a layer one spot closer to the top, press Cmd+] (Ctrl+]).
To move a layer one spot farther back, press Cmd+[ (Ctrl+[).