Ask a club player which conventions a beginner should learn, and watch what happens. You get a list. Stayman, Jacoby transfers, Blackwood, Gerber, negative doubles, Michaels cue bids, the unusual notrump, fourth suit forcing, and somewhere around item twelve you have stopped writing them down.
None of it is bad advice. It is answering a different question than the one you asked.
A convention is an agreement, not a trick
Start with what a convention actually is. It is a bid that means something other than what it appears to say. Partner opens one notrump, you respond two clubs, and you are not suggesting clubs at all. You are asking whether they hold a four-card major. That is Stayman, and it works for exactly one reason: the two of you agreed beforehand that it would.
Which means a convention you half-remember is worse than no convention at all. Bid two clubs intending Stayman, watch partner pass because they think you have six clubs, and you are now playing two clubs on a 3-2 fit. The auction did not fail because the convention is flawed. It failed because it was never really an agreement.
Beginners tend to skip past this part. Bidding is a conversation rather than a code, and a convention only adds vocabulary if both people speak it.
The three that earn their place early
Stayman. Learn this one first. Notrump openings come up constantly, and without Stayman you have no way to find a 4-4 major fit after partner opens one notrump. Four hearts on a 4-4 fit will usually beat three notrump, sometimes by a lot, because the ruffing value is real. One convention, one very common problem, solved.
A strong artificial opening. Most beginners play two clubs as the strong bid, and you need something like it. Otherwise a hand with 23 high card points and five solid spades has no way to force partner to keep bidding, and you end up in one spade making six. That is not a small loss. That is a board you gave away before trick one.
Blackwood, eventually, and carefully. Everyone learns Blackwood second and misuses it third. It counts aces. It does not tell you the hand is worth a slam, and it will not rescue you from a void or a missing trump queen. Blackwood checks a slam you already believe in. It is not a way to decide whether to believe.
The ones that can wait
Transfers, negative doubles, Michaels, fourth suit forcing: all genuinely useful, all solving problems you probably do not have yet. Fourth suit forcing matters when you are repeatedly stuck at the three level with an unclear game try. If that is not happening to you twice a night, the convention is theory, not a tool.
And there is a cost people underrate. Every convention you adopt removes a natural meaning from a bid. Play Michaels and two spades over their one spade no longer shows spades. You traded one message for another, permanently. Beginners collect conventions the way people collect kitchen gadgets, and the drawer fills up with things used once.
The test that actually works
A convention earns a spot when it solves a problem you keep having. Not a problem in a book. A problem that turned up at your table on Tuesday, and again the Tuesday before that.
So pay attention to the failures. You and partner landed in three notrump with eight hearts between you? That is Stayman or transfers talking. Held a monster and had no way to describe it? Strong two clubs. Opponents keep overcalling and you never know whether to double? Negative doubles. Let the hands tell you what is missing instead of working down somebody else's list.
Finding out whether it helped
Now the uncomfortable question. You adopt Stayman, you use it on Thursday, you reach four spades and make it. Did the convention help?
You cannot tell. Not from your table. Maybe every pair in the room reached four spades and made it too. Maybe three notrump was cold for eleven tricks and your shiny new convention just cost you a board. Making the contract feels like proof, and it is not, which is exactly why the same hand scores so differently at different tables.
The only honest answer is comparison. Play the deal, then find out what happened when other people held those same thirteen cards. That is the idea Bridge@Home is built around: your four players sit down at your own table with pre-dealt hands, and the results get scored against everyone else who played the same boards. Add a convention, play a few sessions, and the scores will tell you whether your auctions genuinely improved or merely started sounding more sophisticated.
The takeaway
Two or three conventions, properly understood and properly agreed, will beat a dozen half-learned ones. Every time. Start with Stayman and a strong opening bid, treat Blackwood with a little suspicion, and add anything else only when a hand you actually played demands it.
One more thing, for anyone still early in all this: conventions are the smallest part of getting better. Counting the hand, planning the play, and judging a hand by more than its high card points will win you far more boards than any gadget in the drawer.