Strategy
To win you have to have the lowest score. This is done by winning as many hands as possible, but also by scoring as few points as possible when you can't win. This introduces another strategic hurdle in the game. Deciding when to go for the win, or when to cut your losses and play your high point cards, is one of the most important strategic decisions you can make. Playing to win every time can be expensive, especially if one of your opponents catches you with a couple of two's in your hand.
At the early part of the game, when you still have a lot of cards, especially singles and pairs, you should use the smallest card(s) possible to defeat the cards others put on the table. This will allow you to get rid of your useless little singles and pairs and save your big cards for the crucial moments when you need to control the game.
If you can keep track of which of the higher cards have already been played, this can allow you to fine tune your strategy to make the most of the cards you have. Even remembering which 2's have been played, gives you a significant advantage.
If you have something you know other people can't beat, you can pass a turn (or turns) and see if other people use their large card (but not as large as yours) and then defeat that card with your own. This strategy is used to draw out cards that can be threats later in the game.
Good luck!