Match sets by selecting a group of cards that has an even (0,2,4,6) number of each color dot. For example, the following is a set.
Simplify the cards on the table by reducing cards that are similar
By canceling the similar colors, the two cards on the left yield a single green dot. A green dot can also be found by combining the two right cards. Because two green dots is a set, it is now trivial to see that 4 cards create a valid set.
When there are less cards left in the deck than the set you have found, you have won the game!
Tips and tricks:
If there is a color that only appears on one card, that card can be ruled out of the current set
If there is a color that appears on exactly two cards, then either both or neither of the cards must be in the current set so the cards can be combined
The last set is selected for you automatically because the final cards are always a valid set