Well, GIANT, you must find out for each plane, what it can do well, and what it can't do well. And then, use the first, and avoid the latter. As simple as that (Lol!)
The easiest to fly German planes are the D VII and the Pfalz.
The D VII is THE killer pig - nothing can compete against her. But you'll have to learn aiming good - she reacts immediately on all stick movements.
The Pfalz is a sturdy battle plane; not brilliant in anything, but solid, good firepower, reliable (doesn't stall much and recovers easily).
The Dr.1 is very good for turn fights, and climbs quite good. It can turn flat like on a plate, 180 degrees! But it's slower than most opponents.
The Albatros is a bit more difficult to fly, stalls a bit quicker, and close-to-ground stalls mostly end deadly. But when you invest a lot of time in learning to know her, she's a great plane. Very solid, can take some hits.
In dives, she can escape all the light ones (Nieuport, Sopwith), but don't dive too steep - the lower wing can then begin to vibrate and break!
45 degrees should do fine. When vibration begins, pull out of dive.
The D II was a superior weapon, when it came out, and the D III was again. "Superior weapon" - not "superior plane" ! The Allied can often turn better; Pup and Nupe are so agile, they sometimes look like butterflies, dancing around you. But butterflies are frail - and you got the TWO guns.
A last tactical idea: learn to shoot well. When you can damage every plane in a furball a bit, they become soon less manoeuverable - and then comes your time...