Source: Justin Lall Bridge Professional
Generally I think most players, especially intermediates, play too many conventions. Most of the time they come up too infrequently or have very small gains that aren’t worth the trouble. However, there are a few conventions that are both frequent and useful that most people aren’t yet playing. Here they are in no particular order.
A jump cue as a transfer to 3N in the auction 1m-(1M)-3M. If you think about it, with almost every holding you have in overcaller’s major you want partner to declare the hand. 
Axx, 
AQx, 
Kxxx, 
AKx are the most obvious examples. You give up a splinter to play this, but a splinter in support of a minor is very rare compared to an antipositional 3NT bid.
Transfers after 1M-(X)-? starting with 1N. This is becoming more popular, and for good reason. Losing your natural 1N bid frees up two ways to raise the major. The direct raise is weak, and a transfer raise is constructive. This is very good, because with 3 trumps you always want to preempt the opponents, but you can’t jump to 3 the same way you can when you have 4 trumps. Being able to bid 2 and not have partner game try or jump to game is like having your cake and eating it too. Losing the natural 1N is not a big loss, with 10 you can XX and with 7 you should pass anyways, so you are only losing with 8 or 9 balanced without 3 trumps. In return you get not just 2 ways to raise, but also the ability to immediately show your suit regardless of whether you are weak or strong because you are guaranteed to get another chance to bid. You would hate to have to XX with a strong 1 suiter and be susceptible to preemption by LHO. You would also hate to have to pass with a good 6 card suit and nothing else. Another example of getting to have your cake and eating it too.
Jump cue as a mixed raise after an overcall. This is a convention I see misused all the time. The biggest question is, what the hell is a mixed raise? The best definition I can come up with is a hand too good for a preemptive raise, and a hand not good enough for a limit raise, with at least 4 trumps andoffensive values. With nobody vulnerable if the auction goes (1) 1 p ?
KJxx x xxxx xxxx bids 3KJxx x Axxx Qxxx bids 2KJxx x Kxxx xxxx bids 3
The third hand is a common hand type that is very difficult to show. I see people bid 3 with hands strong enough for a limit raise, and hands that are more balanced and defensive (which should just bid 2) so often that it takes away from the value of having a mixed raise to begin with. You can get to a lot of light games by using these correctly.
Suit Preference in the trump suit. Ok, this is a carding agreement, but it’s a very important one that all top pairs and few intermediates use. The idea is simple, you show whether you like the high or low suit (sometimes the middle is in play) by the way you play your trumps. With 2 just play up the line with no preference. That way only a high low is a strong signal. With 3 play the middle for no preference. This extra signal can make all the difference for the defense.
Invitational jumps at the 3 level after partner opens. These apply when partner opens 1x, and you bid 3y where y is lower than x. This is also only for 2/1 players. The problem is an auction like 1 p 1N p 2 p 3. This could just be a weak hand with long clubs and isn’t invitational, so with 9 to 11 points and a good suit you need another way to bid. I propose bidding 1 p 3 with that hand type. It also protects you from preemption and sometimes has a preemptive effect of its own. Ideally you would have a good 6 card suit and not Hx in support of partners major, but you aren’t always dealt an ideal hand. Just remember partner will pass with a stiff and a minimum, because if he bids anything else it’s forcing.
I think if everyone reading this adds these methods my email will be flooded with thank you notes.
You’re welcome!