Choosing your settings
When you play any FPS on mobile, you should jump into the settings and adjust them so you can play comfortably. First though, try to set your FPS Limit to 60, and lower your graphical settings to hit 60 if necessary. It'll help a lot.
Once you've done that, you should also look at your sensitivity settings. You might find that aiming is either too responsive, or not responsive enough. I set my ADS aiming to be a notch lower for accuracy.
I also set myself to the one-touch ADS mode, as I find it to be the most accurate and helpful when in battle.
Smart use of pick-ups
When manoeuvring around the stage, keep in mind your health and ammo at all times. Your primary weapon has limited ammo - your secondary has unlimited, but is far less capable.
You can collect both ammo and health around the stage, but more than that, you can pick up health mid-battle in order to overcome enemies.
If you walk through health pick-ups while shooting enemies down, you are almost guaranteed to keep surviving, and take down more opponents.
Your heroes all have their own unique abilities, which should factor into your decision making when running into battle.
Several hero characters that you can use have healing abilities, which can give them an edge in TDM - especially Slade, who also has very stable damage potential.
Meanwhile Revenant has the Inner Rage ability, which can nerf the damage he takes, making him a formidable tank, and speeds him up. Choose your character wisely for the best results.
Use the map to your advantage
Of course, as with any shooter, knowing the map will give you an obvious advantage. At all times, you should be attempting to memorise the twists and turns of these mostly-symmetrical map designs, remember where items are, and where good hiding points are.
Objects in the stage, like walls, planters, crates, and more can be used as cover. You can't crouch behind them, but you'll certainly be more well protected than an enemy in the open. Strafing in and out of cover is also a good way to make the enemy waste ammo.
Once you have full knowledge of the map layout and where everything is, you're pretty much guaranteed to be able to kill anyone who remains unaware of their surroundings.