my typical play style, i fly the 190D a lot and sometimes the k4.
typically with the d9 I take full fuel and a drop every sortie. I like to set myself to climb in a direction that will take me just out of the sector i'm going to. Then ill go afk and smoke a cigarette. when i come back I'm usually between 15 and 22k.
if i think the fight is low ill drop to about 15k and pick up speed before i enter the fight.
if i think there might be bombers around i'll head for the fight at 20k or so. I like to kill bombers so its nice to get to a fight at a good alt.
usually ill drop into the fight and slash attack until i get lower e. typically if i'm below 5k and slower than 400 it's time to extend and climb a bit.
i've been pretty successful in the Dora not so much in the k4 
i really like the 190, because the cannons are great, lots of ammo and it takes just a few hits to get a kill. plus with the dora i can usually escape a bad situation, and it has enough fuel that i can leave climb and come back a couple of times.
I''ve just found that i can't get kills as easily in the planes with 6 .50 cals.
not really talking about the k4 that much i cant hit anything except bombers consistently with it yet. but that's my play style.
i also like to use the TA-152 its a fun plane to fly. and 90 30mm is just great.
Maybe next time I see you on you can join my plane and I'll show you how to aim or at least set up the shots to aim the thing. It is very hard to be precise when aiming the K4 because no one really knows how exactly to aim it every time they set up for a shot. I use a 2 second burst on my shots.
What makes the K4 difficult is setting up for the correct shot without blowing all your E or losing all your alt. In a K4 you have to spiral dive on lower opponents to set up a nice deflection shot. In the 190D you can easily dive going 560 and still make a simple lead shot. If you miss, the 190D you can fly away and regain your alt without too much catching you. If you miss in the K4 you have to watch your 6 becuase planes who dive on you might catch you considering you have to cut throttle to dive and may have lossed a lot of speed going for a shot which you missed, and now roll over again and again to kill him, there by losing speed and alt which makes for an easy pick. As triton said, missing your shots suck in the K4 is frustrating as hell and becoming impatient to get a shot will cause you to lose a lot of speed and a lot of alt.
The way to fly the K4 is to beefin up your defensive techniques, again watch my film to see how I fight defensively and turn the defensive to offense without losing too much speed. I use a lot of flaps to get a slight extra lift and to work the vert, potentially rolling around my opponent to gain their 6. As you can see, I couldnt out roll the first spit soo I had to dive, as he was chasing me I used aileron to roll in the direction I wanted to pull up and then when the time was right and I knew the spit couldnt follow (black out), I right snap rolled In to get the shot on the scissors.
Watch my film Jumbo that was posted a page back. I missed quite a few "easy shots" but it is just hard to measure when exactly to shoot.
To be effective in the K4, or any 109. You have to fly about 12-15k max, fly it fast like you are zooming around in the air, and be very aware of SA, set up your shots using spiral dives, overshoots, or ropes (have to get close) (not like how you set up a shot with a 190, unless you rope), become very knowledgeable about defensive maneuvers, timing, ACM, and understanding what your enemy plane is capable of. All of this goes into flying the K4 because it is not suppose to be flown like a 190D or a Brewster.
