Actually this Rakan build is designed for tank build only, as long as all the items and runes are picked exactly for that role, also it is unplayable for mid.

First thing you have to mention while playing on it, is that if you choose Ignite and Exhaust as you'r summoner spells you will have no escape but [W].
So you have to understand when to use it.

Your shield's are not super effective but they can still avoid much damage.

Nevery forget helping your adc even if your team is being carried via other champion.

Your [Q] heal is also not that powerful so don't risk for it's cast.

Use your ultimate only in cases you know 100% that, that is a at least double kill.
Never use it just to damage.

Your passive ability is very powerful if you know how to use it. You can easily iniciate a teamfight with it.

Xayah is probably one of the best picks with you, the [E] range is highly increased and her skillset is very comfortable for you and vise versa.

Samira is second adc you should main play with, your [W] give's her opportunity to get her [R] very fast via passive ability, and your shields can let her live longer in ultimate.

There are some special situations and things that you should never do.
Here are some good examples:

2 v 1 -ing even under your tower.
You will probably get your *** beaten and do nothing but die.
But if you have [R] and [W] you can get at least 1 of them.

Jungle buff farm.
You never have to get any jungle buff, even the blue one.
It is useless for you.
Better 0/10/0 Yasuo to get it then you.

Forget about adc.
Even in case if your game is carried by toper/jungle or mid, never forget about your adc, because you are his support for the first, and then for the others.

Dragon missing.
Your life is not that expensive for your team, so if you see enemy team or jungler killing a dragon, feel free to try to steal it.

Flash on D.
Lol if you use flash on D, don't speak to me...