Apart the chance to have a bad keyboard/mouse setup (other made suggestions about this), you have to consider that WT Air Forces is a game that requires a quite long learning path, so you shouldn't be discouraged by the first difficulties.
Almost any opponent you are encountering now is more or much more experienced than you, so no surprise if they can fly and shoot better than you, even if you would have the best keyboard/mouse setup and fully spaded planes and crews.
There are so many thing to learn at the beginning that I wrote my opinions here:
It lists the most important to-do and not-to-do things for a beginner, IMHO.
Just to mention a couple of them, regarding offensive actions: use both deflection shooting and zoom view when you attack an enemy plane.
For defensive actions, having a bandit at 6 o'clock is a trouble for any player, even experienced, if the enemy is skilled and trained. I put there some advices.