The biggest mistake a lot of home recorders make is to underestimate the ambient background noise in the room. You get used to it and block it out, but a microphone will not!

The hum of a CPU fan, the tick of a clock, next door's dog, passing traffic - one I heard even had a stunt pilot practicing overhead. No kidding!! And that was on a CD they were selling at a club gig!

Another mistake is to record effects (reverb, compression etc) - you can't take them out afterwards! If you think you may need effects, add them at the mix-down stage - and exercise restraint!!

Positioning a microphone takes a lot of understanding - where the sound is coming from, what frequencies are involved and how they drop off (inverse square law), and whether the room itself has any natural reverb are just a few considerations.

A large diaphragm condenser mic will give a much 'warmer' sound than, say, a tieclip mic, and you should do an A-B comparison to see which you need - the easiest way is to put them in the same position and record one on the left channel, the other on the right, then see which gives the result you want.

It takes years of practice, and there are no shortcuts. Every job has subtle differences.