I personally find that I learn best through beatings, perhaps this may help you. After you get beaten down repeatedly by various zoning tactics, you'll eventually find your own way around it and you'll be a much better player for it. However, there are a few different tactics I can recommend (General fighting game strategies, not Injustice specific ones):
Bulldogging - The idea here is to just keep walking forward and block each incoming projectile. Eventually, you'll walk your opponent to the corner, and you'll be in their face. You will eat a lot of chip, but you won't get anti-aired back full screen again.
Jumping - Don't jump excessively, since many anti-airs will send you far away from your opponent again. However, if you make a read on your opponent, you can nail them with a hefty jump-in combo.
Laming them out - Get a small life lead, if possible, then stay fullscreen away. You can react to every projectile they throw, and they'll eventually have to take the fight to you if they want to win.
Armor / Invincibility - Figure out which moves you have that can go through their projectiles, and hit them with it when you predict a projectile. If you manage to hit them enough times, they will eventually throw projectiles more cautiously and you'll be able to close the distance much easier.
However, the most important thing is to be patient. A projectile tosser WANTS you to get impatient, so they can prey on your mistakes and win. Hope this helps.
