Okay, I give up. What is the secret to making a drinkable cup of plain old coffee?

I actually got fired from making coffee at one of my previous jobs (not from the job itself, just from coffee duties). Luckily, my current boss likes coffee that can be eaten with a knife and fork so the fact that mine usually tastes like tar doesn't seem to bother her. She buys Gevalia or something like that and I still manage to make it awful. (We're already assuming that I should use filtered water since Houston's water has a bad chlorine taste/smell, and that you're not supposed to boil coffee.)

Short of roasting and grinding our own, which isn't really feasible in the office, can anyone recommend a least-offensive store-bought brand and offer any tips on how to screw it up as little as possible?