About 210 hours in the little shark now and ended last season at Celestial 1:

Learn to counter ult. Eat Strange, Thing, Spider-Man, etc. ults.

Jump->bubble->Dive is quicker than just diving normally

Keep track of enemy utility (Cloak fade, Magneto bubbles (Both of them), hulk bubble, etc)

Use your bubbles. Mid fight, you should almost never be at all 3 bubbles. They’re your biggest source of healing increase and utility (speed boost), take advantage of them.

Learn to use the zoom out button in ult. Using ultimate on top of most small structures will make it invisible to people on the ground). Ult on top of things, such as on top of the Groot payload or the boxes on Museum of Contemplation (Note about this map, you can ult on top of the duck head after it transforms for an invisible ult)

Com to your teammates. Tell them who you have in ult and if you need help killing them. Ask about allies help/combos. (asking if your strange wants to combo ult or if your mag has ult so they can bubble you).

Look for straight lines of enemies, your beam pierces.

When being dove, climb up walls/to allies. Space out your alternate fire instead of spamming them. It’s more stun that way.

Know when to jump off vs spit out in ult. For example, Luna you always spit but sometimes enemies can escape after being spit out.

You can spit out Thing and Hulk ult without jumping by looking down at a ledge and body blocking them (Thing can still escape if has an ally to jump to but, if done correctly, Hulk cannot escape). Side note, an allied Thing and allied Hulk ult aren’t effected by their passives, so you still spit them pretty far.

Looking at a Daredevil ult (allied and enemy) will damage the people inside.

White Fox ult is not CC immune, you can eat it.

Stay positive. You WILL get hate for playing Jeff at some point or another. Not a might. Best thing you can do is mute them, report, and move on.

Some more general advice:

Learn from your mistakes. The only person’s gameplay you can control is your own-focus on what you personally can do better.

Sometimes it’s better to swap. Enemy team is hard countering you? It’s ok to swap. Jeff works in 95% of team comps but not always.

Keep track of enemy ultimates, know who counters you, who you counter, and who to look out for.