I've converted a few MTB's to touring/commuter rides, and the best thing you can do is get some slick tires, like the Specialized Fatboy, or if you don't have the cash for a fancy slick, most bike shops carry some around $9.99-11.99 that will serve the purpose too. 80PSI+ is good too. Get some nice long bar ends to give you another hand position, plus they allow you to get more "aero" on the bike. A longer stem with about a 5-10 degree rise might be nice too. Not sure what you currently have but for road riding on an MTB I have used some 110-125mm stems. Again, gets you a bit more "aero" on the bike. Maybe throw a rack on the back if you think you'll need it.