Excellent advice is available here and on other forums, but don't blindly follow everything that you read. Stop to think about it yourself, and don't assume that what you read is correct. Sometimes people misunderstand a plea for help. Sometimes people make typo's. Sometimes people are just plain wrong.
Ignore the advice listed above if you're reading anything that Sydney posted. Damn, I miss that guy.
Don't assume that the squeak, click, groan, etc. is coming from the component that it sounds like it's coming from. The tubing used in a bicycle frame can transmit sounds, sending you on a fool's errand, in which you tear apart the bottom bracket to eventually discover that it was your pedal squeaking.
Don't haphazardly approach a problem. Always troubleshoot in a systematic manner.
Don't ignore a problem. If you ignore a small problem then it will eventually turn into a big problem, which cannot be ignored. Fix it while it is still small. It's cheaper that way.
Don't spin the crank or wheel of a fixed gear bicycle to move the chain while you clean it with a rag. It takes more time to individually clean 8-12" sections of stationary chain, but it won't amputate any of your fingers.
Don't cut cables with anything but a proper cable cutter (i.e., one with sharp, notched, bypassing blades). Mechanic's or electrician's wire cutters are made to cut wire -not cables.
Don't find the piece of glass that caused your flat by sweeping your finger around the inside of the tire casing. If you ignore this advice then you will only find the piece of glass after it has sliced your finger open.
Don't ride with loose spokes.
Don't use a cheap, improperly-sized spoke wrench.
Don't use a presta valve in a shraeder rim without also using an adapter washer to fill the space that remains around a presta valve in the larger shraeder hole.
Don't forget to carry a shraeder pump adapter if you run presta tubes, so that a good samaritan (or a gas station) can inflate your tube when you flat out and your pump breaks.
Don't use clear packing tape in place of rim tape. Clear packing tape breaks into little tiny pieces when you try to remove it. You will spend hours individaully removing each little tiny piece.
Don't expect your bike to remain forever shiny and free of scratches. You may actually find it liberating to start using your bike, instead of worrying about cosmetically damaging it.