Cards that add AND subtract points for single veggie types have the highest value, but can also be more dangerous.
Try to focus on two or three different veggies, unless you're going with a wide strategy. (Like the card that gives 12 points per full set.)
Reuse the same veggies as much as possible.
Balance your point cards, you want enough to get points, but not as many as to lack veggies. Aim for 4/5 (Unless it makes sense to move away from it, of course, also depends on player count.)