My passenger side rear brake light blows right after I replace the darn thing. Anyone have experience with this problem??

A little nervous about doing my first front brake pad replacement, but was somewhat reassured I should do the work myself after my mechanic replaced my fuel filter (the connection to hose too tight on one end) and didn't tighten up the bolts that hold the cage to the frame. This is a few months after he didn't see that my water pump was leaking when I told him the heater wasn't blowing hot air. Oh, it's just low on coolant, he said. Well, I'm thinking where the heck did it go then? So I popped the hood..........

So, why should I tell him what needs fixing or fix his mistakes, when I can just take my time, learn something and save some money?

Thanks!