(for those who don't read or care about runes and just take)YOUR HEALING TAKES EFFECT AFTER TAKING AN INSTANCE OF CHAMPION DAMAGE

a lot of healing is based on missing HP

taking light damage on purpose actually heals you, so try your best to take lighter poke damage on purpose while under 60% max HP

They'll run a lot, when you chase them with Q, make sure you can at least land slightly charged W (1/5(20%) at least).

If they got very weak poke skill, try tanking it to proc your healings (after taking champion damage)

With healing, your HP will probably float around 50% and their mana will run out pretty fast.

HEALING ABUSE: walking up to ranged poke champ will probably make him hit&run with light damage, when you start walking away:
1. they go to you past minions, run with Q till you can E them if you're fast enough, if not, just a step or two to scare them and go back. //
2. they keep distance, just get back near your minions and wait CDs.//

after healing bead(1st healing component) I like standing between them and minions to make their life even more miserable for going ranged top lane

stand at least to the side of enemy minions, in a fight they may help charge W a bit faster for slight damage, always keep (rune)grasp up by hitting minions with a basic attack when its CD is about to expire

(UNLESS HP IS UNDER 40%) After asserting domminance in a fight or two, stand between the enemy and your minions.
This guarantees you enemy gank at lv 4 (if its first gank), and enemy will gank you at least 3 times by minute 10.
(IF HP IS UNDER 40%) stand to the side of your minions

After a bit of limit testing in few games, you should be able to tell how much your 2AA>Q>2AA can do damage, if you have enogh HP (depending on enemy laner and jg) to survive with 20% HP, I recoomend hitting them a bit harder than a short trade, the more you stall enemy JG(pumelling him till recall or low HP for only 1 more camp), the bigger JG gap gets. The more enemy JG ganks, the better opportunities your JG gets, when you get a good JG it's a free game.

you cannot kill BOTH in 1v2 when bellow lv 4
At lv 4, IF you got 5+ caster minions + enemies are squishy + you got more than 70% HP = it's doable

Unless a fight is, or goes towards, your river, do not even join.

With Sett's low mobility, you'd at least want some of enemy exits cut off, so if they're fighting in a bush in river near mid, thats enough of an opportunity.
Since enemy JG will stay near top with you showing off and standing on their half of the map, chances are high that enemy JG will join as well, so any fight in your river is important for you as well, but don't even try if your either your mid or jg isn't near , and remember to ping when you start going to give cue to those who don't watch map