Situational awareness. Know the flank routes, lay traps there.
Learn the lob grenades into rooms bounced off walls or other objects, trajectory.
Always, always try to keep one mine in reserve. That is your "oh shit I'm out" mine when you are in trouble or an ult is coming and you need out.
With rip tire try not to ult straight down the line unless you have a visual their backs are turned and preoccupied with your team. Otherwise, flank behind and rip tire OR get up above and ult; seems most don't expect those tires to come from those directions.
Your best thing is to really learn to aim with the grenade launcher. Learn and get used to the arc of the grenade fire to know how high or low you need to aim to get the grenades where you need them.