A preempt is a high-level bid with a weak hand. It takes up valuable space from the opponents. This will make it much more difficult for the opponents to bid to the correct contract.
Basic requirements for a preempt are:
Above the 1 level (with exceptions of NT openings and 2c). In other words, 2♦/♥/♠, 3♣/♦/♥/♠, etc.
6 cards for 2 lvl, 7 for 3 lvl, 8 for 4 lvl, etc..
Less than an opening bid (around 5-10 points)
Good suit quality (2 of the top 3 or 3 of the top 5)
AQxxxx is fine because we have 2 of the top 3 cards (A and Q)
QJTxxx is also fine because we have 3 of the top 5 (QJT)
When to Preempt?
When we do not have a lot of points, preempting is more attractive. With more points, we prefer to start low to give the partnership more space for game/slam exploration. Also, when you have little points, this likely means that your opponents have more points. This is perfect for taking up the opponents’ room!
Preempting is also more attractive when we have a long suit since it decreases the chance of going down too many tricks.
1. ♠AQJ842 ♥7 ♦T42 ♣632
This hand is an example of a 2♠ opening
2. ♠J97432 ♥AQ62 ♦KJ ♣A
This hand is too strong for a preempt, and the suit is too weak, open 1♠
3. ♠6 ♥942 ♦KT4 ♣KQT875
Open 3♣, since 2♣ is reserved for certain strong hands. This bid is not ideal because you usually want 7 cards. The alternative is to pass.