Distracting enemies with one plane while the other attacks an objective is a good plan.
Choose your moves carefully when you learn new ones, for some are more valuable than others.
While you're within a cloud, enemies can't see or fire upon you, although you'll be restricted to basic maneuvers only. Note that enemies can also hide in cloud cover, so make sure you take them down before they can hide themselves safely away.
As a general rule, being higher in the sky is more advantageous than being lower, as you'll have more special maneuver options on the table. There are three altitude heights in total, and unless you're in an engagement, it pays to climb higher if you can.
Missions are split into two different categories in the game - offensive (marked red on the map), and defensive (marked blue). In order to achieve a Decisive Victory in a campaign, you're going to need to achieve seven mission victories.
If you want to earn more points in the game, you can adjust the difficulty setting before heading out on a mission. Note that the challenge will be considerably harder, and the mission may take longer, so choose the difficulty level that works best for you.
It's best to fire on planes from behind, as this makes it difficult for them to turn and counter-attack, and also puts them squarely in your targets. For that reason, it's worth making your combat approaches in wide tactical arcs, using more than one unit if necessary to make sure the enemy is perfectly trapped for an assault.
Note that different sorts of damage will impair aircraft in different ways. Should a plane's engine catch fire, a certain amount of damage will automatically be inflicted upon it during each turn. Wing damage may cause limited maneuvering options - pay attention to the messages received during combat so you can adjust your strategy accordingly.
If you're presented with a series of green firing options, don't just automatically take the one the game has decided is the best (marked with a target icon). Only you know the objectives of the game you're playing, and sometimes it's worth getting a smaller shot in if it improves your maneuverability for the next turn. Always think a few moves ahead of your current options, and execute your strategy accordingly.
Do not be lured into the red areas of the map, as you'll take heavy fire from any surface-to-air defenses in place there. With that said, you can of course lure the opponent into your own territory - two of your planes can be used effectively here to steer the fight in a favorable direction.
Be very wary when taking on rear-gunning aircraft, as these can cause calamity on the battlefield. Bombers, reconnaissance planes, and two-seater fighters all have rear-gunners. These units are best attacked from below or from behind, and with all of the firepower you can muster.