ok i know that to make a mix sound good you need to mix tracks that do not clash, but i am having trouble keying records!

ok i get a keyboard and find the key that best suites the track but do i key the track by the melody? but the melody changes every second!? the bass? how?

someone shed some light on this

thanx

Usually you'll do it by the bassline. You'll find that if you found the right key, it will never "clash" with the melody.
I know the bassline can change too, but usually the first key used is the one. If the bassline changes afterwards, you'll hear it's in a key relative to the original one.