BPM your records!
this can be done on a pioneer mixer. Then just write it on a lil label.
That way you know what goes with what.
mixing hiphop is probably one of the most fun. but they generally have to be really quick due to not wanting vocal clashes unless of course you are rocking an instramental. I always listen to start of the record im about to mix in and then think where it would soung good coming in to the one playing. good luck!