The best place to look is within emacs: with a .ly file loaded get help on the mode ( c-h m ). At least that will give you a list of the key-strokes that will do something LilyPond-ish. By far what I use the most is 'C-c C-l' to compile a LilyPond file and provide messages from the compilation in a buffer (in compilation mode) where I can then mouse-click to get to the position of failure. Typing 'C-c b' or a bar-check character ('|') also gives a beat count in the measure, if you hadn't noticed.
Most of the other editing sugar I like is basic emacs : auto-fill'ing comments, auto-indenting code, multiple windows and buffers, syntax highlighting, etc.
-glen