If you've gotten this far, I would like to remind you that Shen ADC is a ****post build I came up with while bored and thus it should be considered as just that, a thing to play with your friends when you just want to have fun and are not really bothered with winning (there is a reason Sylas support is tagged to be an ideal synergy). That being said, your main tactic is going to be - predictably - abusing the flash spell (and hextech flash) and E ability. The thing I like to do is flash + E at level two. Even if you don't kill, you should be able to do a good chunk of damage while Shen's passive and the Heal spell should (hopefully) keep you alive.

A thing to note about this tactic, though, is that you absolutely can and will not survive if you go in alone. In games where you're not with a duo, I suggest telling the support exactly what the plan is. This strategy is also probably not viable with supports like Lulu who won't be able to neither survive the engage nor deal enough damage or utility to make up for it (her only useful ability in this combo is her ult, every other ability isn't going to deal enough damage or give enough CC to help her and you make it out of the dive alive), but on the other hand, the argument can be made that this strategy isn't viable at all.

After the initial engage, while it is going to be harder to engage again with Hextech flash, harder doesn't mean impossible. Additionally, with it's shorter cooldown it's possible to not have to commit, since nothing will really be wasted. Worst case scenario, you have Cosmic Insight giving you a shorter cooldown on the "good" flash.

And that is going to be pretty much the entire gameplay for you. Whenever you go farm, make sure your passive is up, so when you uninevitably get poked the damage won't be as bad.

Note: once your regular flash is up, there's really no "bad" time to engage. As long as the enemy isn't under turret and you and your support have more than half health, it's possible to go for it, especially with (in later stages) Shen being as tanky as he is. As long as you activate Solari and Randuin's and you won't be greedy, the dive should be advantageous for you.

(Also please don't play this in ranked)