Close to 80% of my work comes from other studios whether it be for mixing/editing/or more production, so here's my suggestions as someone who has seem everything from perfect sessions to unbelievably awful.
1. LABEL ALL TRACKS AND AUDIO FILES!!!!! I can't believe some people don't do this. Label all the tracks and make sure that all audio files have a name. IT's no good to me when I have to spend an hour figuring out what "audio 01_01 through audio 64_09" are.
2. Consolidate all tracks to bar 1. This will unsure that anyone can use the session on any daw. BUT Also save a session of unconsolidated in case you accidently miss a nasty edit. Also, export the tempo map as a midi file. This greatly helps too!
3. Make sure you print everything that has to be printed....VST instruments, SOUND SPECIFIC EQ AND COMPRESSION (like filtered loops or guitars....NOT MIX EQ/COMP), or anything else that direct affects the sound of something.
4. Add a text document with any notes, ideas, problems, or stuff that you think someone would like to know about the project. The best notes I ever got had a tempo map by bar, key changes, and then a breakdown of each section and what they were looking for.
Hope this helps.