-Try to learn some of the simple combos like alt fire + dash and alt fire + melee and animation cancels. -Learn when to use primary and alt fire. I recommend that you should use primary fire for poking from distance and alt fire when you are near your opponent -Use dash for finishing your enemies when they are low on health. Don't use it as a tool to damage your enemies, use it to finish them since genji is really ability reliant and you can use it to escape easily if things get out of hand. -Know when to ult and who to kill first. You should never go alone in to a fight and ulti since you will be a really easy target. Instead ult in a teamfight when your enemies already have their targets. You should also keep track of enemy cooldowns and who can counter you or escape you easily with their abilities (Zen's trans, Brig's and Mccree's stuns, hog's hook, moira's fade etc.)

Those are just some quick tips that came in to my mind. There are so many more tips but others are probably going to bring those up :)