Avoid extended trades with Sett early. He has a lot of physical damage and will win most auto-attack trades. Keep this in mind when trading with him.
At level 6, Sett’s Ultimate R is pretty strong. Do not overextend or stay on low health in the lane as he can easily kill you or set up his Jungler.
Keeping the minion wave closer to your side of the map early on will reduce Sett’s ability to get kills and win lane. If you’re not very strong in the early game, default to keeping the wave on your side of the map.
Avoid grouping to closely as it may allow Sett to get a multi-person E off which will help his team win the team fight. Splitting up slightly will be better for you in the long run.
Do not walk too far forward when sieging an objective as Sett may use his Ultimate R to pick up the closest champion and launch them into their allies behind them. If you’re grouped together and in line with one another, it will be harder for him to do this.
When no team fights are occurring, Sett will put himself in a side lane and try to split push. When he is alone, you could look to either pick him off or start a team fight with his allies when he is unable to help them.
Sett’s laning phase is strong. Expect him to play aggressive and go for early kills. Avoid trading with him at level 1 as he will out damage most champions.
Once Sett is level 6 and unlocks his Ultimate R, his ability to get kills in lane also increases. Watch your positioning and disengage if you’re low as his all-in combo deals a surprising amount of damage.
In the mid-game, Sett will be difficult to fight unless you’re ahead or have assistance. Avoid fighting him and disengage if he runs at you and tries to fight you.