[helene_t]

Here's the simple cheatsheet:
- always bid at least to the level of your own fit. I.e. 2♠ if you know you have 8 spades, 3♠ if you know you have 9, 4♠ if you know you have 10 spades
- bid one level higher is you know opps are in a lawful contract. I.e. if they have bid 2♠ and you know they have an 8-card fit and that you can find an 8-card fit at the 3-level, you should bid.

Then there are all the adjustments, and of course if you think opps have values for game you should let them play a partscore. But the above is the basics.

And sometimes you have to accept that you don't have the information you would like to have, and have to guess. For example, if they bid 2♥ in a certain 8-card fit it is usually (not always) LAWful to bid over it, but you may not have the methods to guarantee that you find your fit even if you have one. You then double with 3-4 spades cards and 3-5 in each of the minors and at most two hearts, or bid 2♠ on a five-card suit. It is dangerous but pass would be more dangerous.