I find I tend to put two cards together rapidly, then look for a third while noting what sorts of 'key' cards aren't present. For example, if there are no three diamond cards of any type, there will be no sets consisting of all threes. Nor will there be any with all diamonds, since the cards don't repeat. So I stop looking for those patterns.
I'm sure there are lovely mathematical proofs for the above, but all I can do is say I'm mostly sure it's the case, intuitivly. Math is so slippery, I can never nail anything down - the minute I assert something positively I wil find I am wrong...
