Well aside from the basic dont drop it on the cement, and do not not shower with it, there is not a whole lot to do. Just dont over charge the battery/batteries if you have multiple.
http://www.airsoftcanada.com/showthread.php?t=26045 <-- Some info on battery charging for the MP7.
The only thing to really clean out is the inner barrel and thats just to make sure its free from obstruction so it does not get scratched or damaged.
If your up from doing it yourself or finding someone to do it who doesnt mind working on AEP mechboxes, crack it open once a year to regrease the mechbox.However before I say anything more I would just like to say that TM aeps like the MP7 usually run very fair and for a very long time if just left alone. Installing high performance FPS parts will only usually work towards decreasing its life span due to enhanced stress on a small mechbox.