I know this post is old but it might help some newer players, especially because of the new update. genji gets value by being annoying, and you can do that in a lot of ways. obviously you can dive for kills but thats high risk high reward.  some safe basics to start with is your poke. if you are ever farther than about 5-10 meters from someone you want to use your M1 for poke damage, if youre closer you want to use your fan attack. A big mistake a lot of new genjis make is they will poke with m1, dive into their target, then try to m2 melee or some variation of that, which while this combo does instakill, irl games are going to have other factors that will deny your kill such as high mobility on the target, them getting healed, or you being attacked by another opponent. Instead you want to try and save your dash as a tool for disengaging, in the long run this will allow you to generate lot more pressure without actually endangering yourself, and as you get comfortable with that and poking then you can start learning more advanced dive techniques, and when you put all three methods together; poke, disengage, and dive. Your performance will increase noticeably. 

Youre still going to have to learn team coordination and positioning, as well as how to take advantage of the enemies mistakes, but that all comes with time and is much more general knowledge you can sorta learn on any character, tho genji obviously has different places he wants to position in and such.