Fight in spots where a minion line lets E stun, then spend W once grit is actually stacked and they are still in front of you; Sett gets much scarier when AA-AA-Q, facebreaker, and Haymaker land as one layered trade instead of three separate buttons
An ugly lane is still fixable if the other top laner has to keep paying health and space to farm near you, but once you fall far enough behind that they can walk up without respecting punch range, Sett loses the part of lane he is built around
In fights, R is often best used on the biggest body that gives you a real landing for multi-man E and centered W, and from behind you usually help more by mauling the diver who crossed the line than by tunneling on a backliner you cannot honestly reach
Use R when it solves the next half-second of the fight, not when it looks coolest. In lane, that often means ulting after they have already committed so you can keep them in front of you for E and a centered W, or using it to throw them back into your wave or tower space. In teamfights, the best target is usually the body that gives you the cleanest landing, not automatically the squishiest champion. If ulting the frontliner lets you hit multiple people with E and cash out grit, that is a good ult. If the backliner is technically visible but reaching them breaks your whole combo, keep the ult for a more honest target.
Sett's basic attacks alternate between left and right punch. Right punch is slightly stronger and faster. Sett also hates losing, gaining additional health regeneration based off of his missing health.
Sett's next two attacks deal additional damage based off of the target's max health. Sett also gains Move Speed while moving towards enemy champions.
Sett passively stores damage he takes as Grit. On cast, Sett expends all stored Grit to gain a shield and punch an area, dealing true damage in the center and physical damage on the sides.
Sett pulls in all enemies on opposite sides of him, dealing damage and stunning them. If enemies were only on one side, they are slowed instead of stunned.
Sett carries an enemy champion through the air and slams them into the ground, dealing damage and slowing all enemies near where they land.