To prepare, you really just need to pick a fast, yet moderately strong dragon. Something like Fury or Skat will do. The reason that you need a fast dragon is that it helps a lot to be the first one on the field and in the game.

I personally prefer Skat because of his "R" ability. The shockwave is very helpful and can give you a slight advantage over Fury.

What you need to do is simple, yet slightly complicated at the same time. Really, your goal is to get behind the other team and pick up a few kills. But how you do this is easier said than done. My preferred way of doing this is going around the side, low to the ground barely scraping through the trees and over the ground. Make sure you're right along the side. The problem with this method is that you can take damage from hitting trees or the ground, which can make it easier for the other team to kill you.

If you don't stay low and fly higher up, you run the risk of getting spotted and the plan won't work most of the time. Just follow my plan and you'll be gathering kills in no time.

With the 2 options, although you know which one I am recommending, the higher option has some uses too. Let's compare them.

Option 1: Flying low

Pros:

Undetected most of the time
Almost guarantees it working

Cons:

May hit ground and lose some health
A bit slower

Option 2: Flying high

Pros:

A bit faster
No risk of hitting things

Cons:

Easily spotted (unless you stay behind things)
Plan won't work as often

So, it's up to you. Pick your plan and go. The thing that will ruin it most often is if you bail halfway through because you see the whole enemy team lining up to attack.