When partner opens 1NT, often the first priority is to explore a major fit. There are a variety of ways to do it depending on the nature of your major suits. Stayman, Transfers, Texas transfers etc. So which do we use, and when?
The key step is to look at your major suits and look whether you have 4 card suit(s), 5 card, 6 card, or a combination. There is also something to do with 3 cards, (in case partner has 5). Lets look at examples.
Partner has opened 1NT and you have both a 5 and 4 card major.
The key ideas are as follows
Lets start off if you ONLY have 1 major, not both
a) With a 4 card major - use stayman. For example
We have 11 points, we are happy to play in 3NT, however first it looks sensible to find out whether we have a 4-4 spade fit. Simply bid stayman, 2♣, and then follow up with either putting partner in 3NT or 4♠.
b) With a 5 Card major - transfer
Here we Transfer to spades. A transfer invariably should show 5 cards at least. Thats useful information for partner to have, the bidding would typically continue like this
You have said to partner - I have 5 card spades, and am happy to play in 3NT. So now, partner with 3 or more spades, can bid 4♠. Note that there is no reason to avoid 3NT, thoughts like "I have nothing in clubs" is just destructive thinking - your side has say 26+ points, trust you will be fine in 3NT if 4♠ is not appropriate.
C) With a 6 card Major - Either Texas or regular transfer.
With 6 cards we can bid Texas transfers (see article on Texas). Or alternatively we can sometimes just transfer.
a) With no slam interest, we can often just Texas transfer
The 4♦ bid shows 6+ spades, and is a quick way to get to spades and hopefully shut out the opponents in case they have a big fit on. But make note - some players agree that Texas shows a slam try, if your partner is like that, then you cant bid like that as they might put you in slam with this weak hand!
b)With a shortage and a slam try, it may be better to transfer normally and then splinter, like this
d) With 3 cards - puppet stayman
The modern way is to freely open 1NT with a 5 card major. We use puppet stayman to ask the NT opener if he has a 5 card major if it is appropriate for us. For example
Here we have asked partner if they have a 5 card major. Partner said yes, 5 card spades, and we decided to play in 4♠ at the end - our hand looks useful for that, enough points and two doubletons.
Lets now look when you have BOTH majors
The main tool you will use with both majors is Smolen
Smolen goes like this, you start by bidding stayman. If partner shows you a 4 card major, great you have found a fit (remember you have both majors to use smolen). IF partner does not have a 4 card major, you jump to the 3 level in the major you DONT have. Lets make this easy with an example
In this auction we started off with stayman, hoping to find partner with a 4 card major and then just raise it to game. When that didn't happen, we bid 3♥ (the major we don't have) to show 5 card spades. Now the 1NT opener can bid spades, declaring it - that is the main reason for bidding the one we DONT have. Check out the article for a more comprehensive look at smolen.
When to not look for a major fit at all
The main time I would suggest is with 4333 shape. With that, forget about the major, and just play in NT at the appropriate level.
Conclusion
overall typically the most important thing we should do when partner opens 1NT is to look at our major suit holdings. If you can generally associate stayman with 4 card majors, transfers with 5 card majors, you will have overcome 90% of the battle. Try keep it simple, smile and enjoy the game.
Read next: System Over 1NT: Transfer Responses and Conventions · Stayman Convention · Puppet Stayman - All you need to know · Smolen Convention: Show 5-4 Majors After Stayman