if you listen to all dance music, it always changes 16 or 32 or in multiples of that. put any record on the decks and count 16 or 32 from the first kick drum. then you'll hear a change. ie a hi hat will come in or something will happen. applying this rule to every record, it means that when you mix a record in you wait until that change on the 1st record, spin the 2nd from the first kick drum at exactly the same time and then both records will change together. swap the basses on one of the changes.....