My process with the teaser trailer was getting the inspiring songs in my head, imagining the songs while in-game and then going back out and opening Sony Vegas after capturing some epic battle shots (I didn't have too much footage to work with, but enough to get the job done). I got more footage than I needed to initially, but you always want a little extra with stuff like this. Okay, so my epic shots are done.
Create a few video tracks, slap them down. Lower the audio from the game footage a little bit and slap the music you were listening to under a battle clip, then it just starts splicing together at an even pace. You sometimes need to move footage around. Then at the end you add your titles, effects, and extra sound effects. Render it, watch it to see if it comes out okay on brightness in a video player, if not fix it, re-render. If something's still quite not right, go back and fix a couple more things. It's a trial and error thing.
Different directors and editors have different styles and different minds when it comes to this, so artistic view may vary.
For this trailer, I used different pieces of audio other than the footage's individual audio (that's obvious huh?).
I used different audio layers to achieve this and changed the volume on each so that there's a nice artistic audio balance as well. You don't want 3 different audio layers making your ears bleed, right?
Anyways, these were my music tracks:
The Motherland - Frank Klepacki (Red Alert 3 soundtrack) [the intro and initial scenes of battle]
World of Tanks Battle 2 [when the battle picked up]
Darth Sidious - John Williams (Episode 1 Soundtrack)
This was my sound effect audio track:
Intro dialogue to Star Wars The Clone Wars movie.
My own mix of blasters, gunships and explosions from a Clone Wars era battle track I mixed.
Just so people were aware of my materials.
Titles were simple: TV simulator and different colors do wonders for hologram style things.
Clip transitions: Soft flashes and some fast fades.
Clip modifications: Brightness and Contrast settings, Pan and Crop (mainly panning and zooming).
So there you go. That's how I made this trailer.
Most trailers will be this easy depending on what I want to do, however some later ones WILL be more involved...don't worry.