The first thing to keep track of in a game is to know where everyone on the opposing team, as well as everyone on your team is located in the arena, however its more important to know where your teammates are then where your opponents are. If you know where your teammates are, then you know where your opponent is not, this helps you make the area where your opponent could be smaller which leaves you less prone to be double teamed, snuck up on, or just flat out being hammered by a better player. If you do run into a situation that is too much for you, knowing where to find help is a very useful tool.
The time left in the game is also something that is essential to keep track of. Each player gets a bomb every minute on the minute i.e. 13:00, 12:00, etc, and since in many games you can't have more then 1 bomb at a time, throwing them proficiently at the right times will definitely improve a player. You should also know how much time is left till you get your next bomb because if your being triple teamed or your attracting attention from multiple players of the other team knowing how much time is left till you get your bomb will help you make your decision to either stay to fight them or run out of harms way, for instance, if there are 10 seconds left till you get your bomb and you have 3 people shooting at you, try to hold your ground for the 10 seconds because when you get your bomb you can kill them all in one shot, however if you have 50 second till you get your next bomb you might want to get away from the 3 on 1 because holding off a 3 on 1 for 50 seconds is nearly impossible. Remember also that your opponents gain bombs at this time, too. Lastly knowing when your next base hit is available certainly useful when your team is trying to destroy the base.
Keeping track of players who are hit or
"down" in the arena is also a very effective weapon to use in a game.
If you know your opponent is "down" look around and see if there are
any of your teammates that you can help out by either hitting the person trying
to shoot them or just by firing at the person to distract them from there main
target which was your teammate, all great players do this but not only do this,
they also keep track in there head how many seconds it will be till the opponent
that is near them is able to fire again and a good player will shot the opponent
that is near by, then look to help other teammates and then return his/her
attention to the nearest opponent right before he is able to fire again.
Knowing the state of your opponent is also important.
The number of shields your opponent has dictates your strategy against
him/her. Often on the offensive when your opponent is on relatively low
shields is advisable. Also whether your opponent has a bomb has its
advantages. Your opponent obviously cannot throw a bomb nor counter yours
if he doesn't have one. Thusly you can be prepared for what might be
coming.
Good luck.