First, decide how many colours you want, too many and it looks like a curcus, not enouph and you won't have the desired effect. Example - If you decide on four colours and you want a balanced amount but to apear random, you would run your first row say 1234-1234-1234. You would then stagger the second row trying not to get two tiles of the same colour touching and so-on and so-on course after course. Depending on how many colours you choose, you may get two of the same colour touching here and there as part of the pattern, but the overall effect will look random and very nice.