1) Restrict the number of restricted cards you can use
Any Deck (+sideboard) can have a total number of 10 Restricted Cards in it. When I first started to play vintage, we made jokes about the decks almost being Highlander, with all the restricted cards running around. If any deck can use only 10 restricted cards of choice, you hurt almost every deck (true, combo a little more, but Banned and Restricted cards hurt combo anyways). Most decks end up with 5-10 empty slots which have to be filled and the decks become more interesting. More interesting decks, more interesting metagame.
My GAT list only runs 11 Restricted cards. Flash runs 9.
2) Play with 70-card-decks
If every deck needs to contain at least 70 cards instead of 60, you have again a lot of deckslots that need to be filled.
The more cards you use, the more likely you are to get land screwed.