I have a cheap/crappy Magna mountain bike and I'm looking to make this my commuter project bike. I do not know too much about bikes since I just recently started riding, but thought if I worked on making this one better over time, I'd learn a lot about them along the way :] Now the problem is, I have no idea where to start.

My commute is only 6 miles each way on rough urban roads. There is only one little stretch on a bike path that's smooth. The rest of the ride is dodging sewer drain drops and other random road debris.

Please help me learn the ways! Thanks!