This build works for all supports but i started doing it with janna so it's gonna be on janna.

This is something i don't take care much but these i think would be the best (Here throw in any runes that you use for other supports).

These are very good you start with health regen and hp OR mana potion (depends on you i pref hp cos you gonna get hitted hard). going to classical philosopher stone, and boots lvl1 and then kage's. Doran's ring is optional but is good (you sell it later when you think you don't need it, just like kage's). Then for some hp and mana (you need those very much) rod of ages, then rabaddon's wich is for all ap champions, and then morello for mana regen and cd (here can go deathfire grasp too). Then one defensive item frozen heart if enemies are ad (and gives nice mana and cd) or banshee's for ap enemies (and nice hp, mana and bubble). Here can go aegis if they are mixed. And shurelia is optional, here can go aegis maybe (if your cdr is 40% capped).

Classical support masteries with cdr maxed out and mana/exp/gold too.
Scout and awareness are useful too but i don't buy much wards so i dont use scout, and awareness can go instead of cdr in offensive tree.

This is just for janna ofc.
You can start with shield too but you should take all 3 spells till lvl 3 becouse of maximum help to your team (that knock up of q is cute, and slow/movement buff is too), and then max your shield as fast as possible becouse it gives nice shield AND ad buff for your ad carries :D. Then max W for move speed and slow (your team could use another good slow eh?).
Ofc. take ulti when you can this is your main support spell.

Clairvoyance is classical for all supports.
Instead of flash you can use clarity and heal, if you think you'll run oom, or gonna need some extra support spell, but i think it's unnecessary.

You probably aint gonna have many minions so that's why we need gp5 items on start.
Except if you go mid (which are rare occasions) then you take all the minions you can,AND get the gp5 items ofc.

Supports i don't play much, but when i do I use this build and I do pretty well (I don't have any ss's sorry). Janna is my favourite but any support is good support so don't hesitate to use this build on any support.