Make sets of fish crackers at snack time...  Use marbles, rocks or anything else around the house for practice.  Just be sure that the set pieces are all the same, so it doesn't cause confusion.  For example, don't have part of the set be rocks and the rest be marbles... Skittles and M&M's work too, but I'd save these for a special math reward.

Remember how to set it up and do it:

• Make one set of the same kind of object
• Count how many are in the set
• Decide how many you are going to take out
• Write out the problem (like 8-3=) << optional step
• Take the objects out and put them off to the side
• Count how many are left in the set
• Write down the answer << optional step

It's a good idea to keep the numbers small when working with sets...  At first, keep the starting set at 10 or under.  Then, you can go higher.  I wouldn't go over 20 though, since the initial count gets to be a "busy work" pain.

The goal is to get the basic idea of taking things out of a set.  Then, you can move on to using subtraction flash cards for memorization of the 1-10 subtraction facts, to The Number Monster for subtraction fact practice and to the next lesson for even better understanding and mastery.