As a professional, make sure you can perform your songs as effortlessly as possible
Can you play your part from beginning to end without any other performers?
Can you play through your part multiple times, slight variations are a good thing, without frustration?
Does it feel natural and not forced?
Do you feel that you can live with your performance?
Working with an engineer
If the recording/mixing/mastering engineer you are working with, even if that person is you, does a great job, thank them by crediting them on your song(s)/album. Digital streaming is here to stay and everyone deserves recognition #GiveCredit and spread the word about your engineer as most work they receive is through referrals.
When you are working creativity, after time, your level of creativity diminishes. Take breaks by leaving the room, taking a walk, play with a pet, etc.... Anything that isn't related to what you are creatively doing. This will clear your head and rejuvenate you and then you'll be ready to go for another 1-2 hours. Take multiple breaks throughout the day.
Whoo Who, Party Time...Excellent...
Good luck the next day if you partied way too much the night before. You should have your head in the game, in this case - the music. Having a hangover, or still under the influence of the night before is not going to fair well for you or the project. Take this seriously and save the party for the night of your final session and your release party. Don't let yourself, and others involved in the session, down.