Yes I know there is no such thing as a shortcut in boxing...but... What simple things made a real difference to your boxing? Shifting weight back and forwards has opened up a lot of things for me for example.
One thing that has helped me with sparring stamina is practicing staying in range and using pivoting and head movement instead of shuffling or retreating when not punching. Not by any means a 'shortcut', but a technique I've used to be elusive without expending all my energy skipping and shuffling.
Pushing off the back foot to put power into jabs and straight rights. Throwing punches one after another, instead of waiting to see the outcome of each individual punch.
Switch hit and throw the straight left straight away lands at a very high connect percentage as it takes my opponents by surprise as there not used to seeing a punch come from that direction and its very fast.
Small, quick steps in any direction. Short straight punches. Keeping the hands high and chin behind the shoulders. None of the "I naturally drop my lead hand" ****.
Learning to push an opponent to the ropes and then keep him there while changing range. i.e. shoulder him to the ropes while throwing body shots. Throw to the head when he hits the ropes, then drive your body into him and throw some body shots. Step back while jabbing and look for the right hand, then get right back on him. Use your lead leg to keep him pinned. Just learning to fight rough has worked for me.
Oh, also: Throwing unorthodox punches. My favorite thing to do is step to my right, dig in with a left uppercut to the center of the body, and then come up with a hard hook to the nose. In addition, a chopping right to the side of the head is a great punch to throw. It's very disorienting to be hit from punches you can't see.
Recently, while sparring, I was in with a quicker guy. He was flurrying on me until I hit him with that chopping overhand right. It spun his head gear around and wobbled him. :thumbsup
not really a shortcut...but I always feel sharper if I start a shadow boxing session with my main focus being footwork first