Erich Hartmann, Me 109 pilot, Jagdgeschwader 52 
Highest scoring ace of WWII with 352 victories; shot down 18 times but never wounded

Once committed to an attack, fly in at full speed. After scoring crippling or disabling hits, I would clear myself and then repeat the process. I never pursued the enemy once they had eluded me. Better to break off and set up again for a new assault. I always began my attacks from full strength, if possible, my ideal flying height being 22,000 ft because at that altitude I could best utilize the performance of my aircraft. Combat flying is based on the slashing attack and rough maneuvering. In combat flying, fancy precision aerobatic work is really not of much use. Instead, it is the rough maneuver which succeeds.

Erich Hartmann, Me 109 pilot, Jagdgeschwader 52

If taken by surprise, I would do one thing or another automatically, depending on conditions. If I had time and saw my attacker coming in, I would wait and see how close he would come before opening fire. If he began firing at long range, I could always turn in to him. If he held his fire, I got ready for a real battle. Even against good competition, you could always break away by using negative Gs. In a tight turning maneuver, the attacker must turn more tightly in order to pull lead on his quarry. For a split second you pass under his nose and his line of sight, as he tries to line his guns up ahead of you. It is precisely at that moment when he gets his gunnery angle on you that you push the nose forward, kick bottom rudder and are gone. Your attacker cannot see you. He is intent on pulling lead and is turning in the opposite direction, in an even tighter circle, even as you are diving and turning the other way. As I said before the use of the negative G is a last ditch measure. Frankly, I tried everything possible never to be placed in such a position because if your attacker had a good wingman, he could quickly pick up that maneuver. This is why I avoided dogfights. They were long and drawn out affairs, requiring all your attention, allowing another opponent to jump you. They were the longest and most difficult method of getting a kill, the expensive and most dangerous. 
 

Erich Hartmann, Me 109 pilot, Jagdgeschwader 52

The key to the approach was simple: Get in as close to the enemy as possible. Your windscreen has to be black with the image, the closer the better. In that position you could not miss and this was the essence of my attack. The farther you are from the enemy, the more chance your bullets have of missing the target, the less the impact. When you are close, and I mean very close, every shot hits home. The enemy absorbs it all. It doesn't matter what your angle is on him or what position you are firing from, it doesn't matter what he does. When you are that close, evasion is useless and too late. It matters not how good a pilot he is. All his skill is negated, you hit him and he goes down. I would say get in close, there is no guesswork. 

Ernst Schroeder, Fw 190 pilot, Jagdgeschwader 300

I catch sight of the glittering reflections of the sun on the uncamouflaged American bombers, off to the left and at the same altitude, about 25,000 ft. Still a long way away, the stately enemy formation crosses in front of us from left to right. I carefully search the sky for enemy escorts but I can make out only three or four condensation trails above the bombers. Curving around, the Sturmgruppe is now directly in front of me, about 150 yards below. I have a grandstand view of the attack as it unfolds. The bombers open up with a furious defensive fire, filling the sky with tracers as we move in at full throttle. At 300 yards, the main body of the Fw 190s open up with their 20 mm and 30 mm cannon, the murderous trains of high explosive shells streaking out towards the Liberators. Within seconds, two of the giant aircraft have exploded into great fireballs, while several others have caught fire and are falling out of formation. On either side of me my Schwarm comrades fire like mad and score hit after hit on their targets. Looking around, I see the sky is like a chaotic circus; whirling and fluttering pieces of aircraft, and entire wing falling complete with engines and propellers still turning, several parachutes and some of our aircraft battling with the few P-38 escort fighters that have reached us.

Leader role: The attacker is the LEADER:

1: Hunt: Hunt the enemy craft, search for the highest energy enemy craft, gain advantage

2: Perch: Perch over and behind enemy craft

3: Press: Press the enemy's energy down by repeated attacks

4: Attack Attack and DO NOT lose energy.. signal to switch roles is EXTENSION and CLIMB behind wing

5: Switch: To Wing role ready to defend new LEADER

Wing role: WING:: The WING is the leaders SIX cover and potential LEADER

1: Perch: Perch on the LEADER rear and higher behind for energy

2: Watch: For leader SWITCH signal: Leader attacks, then he extends to climb and perch

3: Switch: Switch to LEADER 

Explanation:

Leader is lower and wingman is higher behind him.

Leader hunts for enemy high cover craft, this enemy craft has the highest energy state

Leader has ultimate decision on which craft to target.

Leader attacks the highest enemy first, pressing him down into lower energy state. Wing follows leader keeping higher behind in surveillance/ assistance mode.

As leader exits attack and extends for height, this is the signal for WING to switch to LEADER role, this allows time to climb and perch, and gives enemy no time to recover. Second benefit is that it is easy to learn for new pilots.

Third benefit, this tactic does not require a working radio link. but it is better to have one of course.

Boelcke's Dicta GruppenFuehrer Oswald Boelcke 1915

Rule 1: Try to secure advantages before attacking. If possible, keep the sun behind you.

Rule 2: Always carry through an attack when you have started it.

Rule 3: Fire only at close range, and only when your opponent is properly in your sights.

Rule 4: Always keep your eye on your opponent, and never let yourself be deceived by ruses.

Rule 5: In Any form of attack it is essential to assail your opponent from behind.

Rule 6: If your opponent dives on you, do not try to evade his onslaught, but fly to meet it.

Rule 7: When over the enemy's lines never forget your own line of retreat.

Rule 8: For the Staffel: Attack on principle in groups of four or six. 
When the fight breaks up into a series of single combats, take care that several do not go for one opponent.

This system was invented by GruppenFuehrer Boelcke in WW1, he then had Richtofen and Immelmann as students.They further refined it, becoming the top aces in WW1, with the best kill/loss ratio.. The new pilots were allowed to attack, gaining experience, with no fear that they were not covered from behind and protected. Of course, in the first battles, it is important to score some kills early, as Richtofen said,

"It takes a few early wins to learn how this trick is done"

"If Boelcke was with you, you felt perfectly safe"