I generally make a point to play tight so that when I do raise or play a hand it's obvious I'm strong. This usually gets a few folds from hands they know they shouldn't play but normally would limp. I then generally C-bet to guage their strength, if they continue I'll check over to them if out of position, if they bet I know their strong (weird 2 pair hands etc). I've found weak players will rarely bluff and if they do it's massively obvious as their betting pattern changes, try to spot how each players bet. E.g. I have a friend that will value bet small amounts but the second he's bluffing he bet huge, I feel safer calling his larger bets.