Hit your rolls more consistently, dont waste roll if you're low health you'll just die, if you have starpowers, steel hoops + recoiling rotator is by far the best combo with darryl. Dont waste ammo as well, when you roll make sure you have at least 1 ammo minimum, preferably 2. Dont hold super a long time before you use it you'll just give your intention away and the enemy will retreat behind a wall.
Dont play passively in neutral, you'll just lose the mid really quickly and be pushed back. Darryl is actually pretty decent in neutral with a 6 tile attack and 7000 health so you can definitely put some pressure out.
If you're playing BB, his roll is 7 tiles and the ball is kicked 7 tiles so its pretty good, especially if enemy goal is open you can score a quick goal. Play more aggressively.
If playing Heist, play more passively, never go onto safe if theres 2 enemies still alive, you'll just die. Try and roll and get a kill and then go onto safe.
The only other mode I'd recommend darryl on is Siege, hes very underrated there imo.
Other than that just play him a lot and you'll learn good and bad matchups as well and you'll naturally get better positioning and roll accuracy. One matchup I will comment on though is the tick matchup, ticks never expect it but you can roll through tick head since darryl doesnt take any knockback while rolling so keep this in mind..