Basically matchpoints scoring works as follows - you get points every time you beat another pair's score. It doesn't matter how much you beat their score by, whether its by 500 or by 10. If you score 110 for making 2♠, and the majority of the rest of the field is in 1NT making +90, you may get a very big score (100%) for the board, even though the difference is only 20. Even if you were doubled, making +470, it may not make any difference to your score as you were still beating the field with your previous score of +110 if they were all on +90.
IMPS works on the HOW MUCH you beat the other players' scores by, so for example, if you beat another player by 20 it will be a very minor difference that won't impact your score much, whereas if you beat them by 500 it will be a major plus to your side.
Pro tips for matchpoints (the most common scoring method for duplicate pairs)
1. Be conservative. Don't push too high if you risk going down.
2. Be aggressive in part score battles - don't let the opponents play in a fit on the 2 level, push them to the 3 level.
3. Avoid playing game in a minor, it doesn't score well.
4. Focus hard on making over tricks yourself, and not giving declarer over tricks.
Pro tips for IMPS (traditionally used in teams scoring, but also in lots of other pairs tournaments - check with the tournament director before play).
1. Push to games, particularly vulnerable games. Even if games are 50/50, it is worth being in them.
2. Generally don't double your opponents if they are in a partscore, unless you're 100% sure they are going to go down.
3. Don't risk your contract for over tricks.
4. Try to take declarer down, even if it means taking risks that might give declarer over tricks.
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