In matchpoint bridge it is very important to be disciplined in pre-emptive bidding. Opening bids of three or higher should show no defensive tricks outside the bid suit. The preemptive bidder should be able to go down no more than three tricks if his partner has a bust hand in favorable vulnerability and no more than two tricks in equal vulnerability. In unfaverable vulnerability a player would need to be within one trick of his bid.
Once the opening bidder makes his bid he should not bid again unless forced to bid.
The responder can add to the preempt by raising the bid suit by the number of offensive tricks he thinks his hand can contribute. For example three trumps and a void will likely produce two tricks. He can also sacrifice against a slam if he has four trumps and no defensive values.
He can also raise the bid to game if he has enough tricks to produce a game.
Some examples:
With both vulnerable South opens 3 and West doubles
1. North holds 3 10987 KQ876 Q87     Bid 5. The opponents can probably make about 4 or 5. Make them guess how high to go at the five level. Your partner will probably go down two or three in 5.
2. North holds void K10987 876 Q87654    If partner is not cheating on his opening 3 bid the opponents can surely make 7 so you should bid 5, 6, or 7. (Sometimes a bid of 7 will push them to 7)
3. North holds 9863 K9 AK6 A87654    Bid 4Partner should be able to make it easly.