Remember to help your team with ganks and dont forget to use avarice blade to farm like hell :D
also note that each 15 minnion kills = 1 champion kill so if you want to close the gap start kiiling creeps so you are able to carry, if killing waves is impossible due to gank attempts, go all the way to the oposite turret and try to backdoor after you farm, if they arrive, you need to activate both highlander and ghostblade to run away like nothing happened XD
It works trust me. If you are in a teamfight never try to go alone to kill everyone, remember that you are an assassin, your job is to focus the carries, not the tanks otherwise they will kill you easily. Stay in the teamfight position of behind the tanks, you are also squishy and if 2-3 people focus you you will be screwed. Remember to always keep ghostblade and highlander out of cooldown so you have them when you need them, don abuse these abilities. If you encounter a mater yi that does not use ghostblade, rush for it and get as much gold as you can from farm with avarice blade and alpha strike+ basic attacks, then try to assassinate him when he is alone, he usually is seperate from his team to get kills, gank him in the jungle if you know where he goes so be map aware as well, if you can get an esy kill go for it, its your job to get fed as soon as possible and shut down all the enemies one by one. Ghostblade the gap closing item for master yi, if you want to 1v1 someone use both ulty and ghostblade, dont use it to arrive somewhere fast, use it most often to escape and to 1v1 someone and run away in the jungle to the nearest turret. Also in laning phase font forget to use alpha strike to either harass or farm and avoid being harassed, alpha strike makes you untargetable for a moment.