Yes, use your wall to separate enemies. Dont always use the healing ability just for healing use it to bait out other abilities like mcree flash, zarya bubble, scatter, doomfist movement abilites, youll win most one v ones unless you cant aim
Try to keep enemy positioning in mind. Like someone said earlier, cryo is best used to bait attacks out. But your timing needs to be on point. (I need to take clips and email blizzard about some mei bugs..) you APPARENTLY can get hooked out of cryo if not timed properly. Regardless, if you keep positioning in mind, know where your team is and CALLOUT targets you can make things work well. I like to play shot caller when I’m mei cause I can turn the tide of a fight with one wall.