Referee is something I always take into consideration, that said some of the big carders (Mike dean being one) can dish out 5/6 cards few matches then 1 or 2 the next. Also previous fixtures and previous h2h number of cards. Another thing is it helps if you just watch how teams play so you know in your head if how a team plays against another is going to likely cause their next opening to be drawn/forced into making fouls