Take all the bits that make your game look cool. Make a trailer from them. If you don't have enough bits, then you have to pad it out somehow, or make more bits.
You don't have to spend a lot of time or money if those bits are good enough. Even the best games out there might only have a few minutes of actual cool stuff to show or do. One classic example of this is Halo, you can take Halo and boil it's gameplay down to 30 seconds of coolness... throwing a sticky nade at a grunt and watch him run to his friends and blow them all up, pistol whip an enemy then shoot them in the head, blow a warthog to hell, hijack a ghost... all those little bits of gameplay add up to about 30 seconds. Feature all of it in a trailer, and people did go crazy, and Halo is huge.
If it works on a massive scale for games like Halo, Battlefield, COD, Farcry, Crysis, Bioshock... well it'd work on a small scale for you. Show the coolest stuff, show it quickly, make it look like your showing random gameplay but actually show the best gameplay your game has to offer.
More important than what your trailer contains, or how long, or anything really - is how your trailer will actually be shown. If your thinking about just posting it on your channel and hoping people get to see it... well forget that, it's pointless. Not unless your planning on getting it featured in the newsletter. For any trailer to make a decent impact, you have to get your YogsCast type videogame bloggers showing it. Make a trailer that other people will show, not just yourself. It's actually more important that your trailer is noticed for some reason, than just making a great trailer. It might actually be more beneficial to make a weird trailer than a great trailer. An amateur trailer is a bad idea - it either has to be really good, or really weird - reasonable is not a word that convinces potential customers.
Some ideas to loosen the mould, so to speak...
* Add in some funny quotes from people... recognizable names or brands, even if they are just saying 'WTF is ?' - that's better marketting than quoting people that nobody has ever heard of.
* Don't use dubstep. That train has sailed. That ship has flown the coop... Dubstep nowadays just screams 'Look kids, I don't rate my own games appeal enough to just show it, I need the wub wubs and troll comments to fit in here'.
* Don't use Inception style orchestra hits. Not unless your game is so awesome that it'll put a white streak in your hair. It's overused, much like Dubstep and Deadmau5 and Malufenix.
* Make sure your text font is exceptionally neat, don't slouch at all with text, especially if it's one of those tell-them-something then-show-them-stuff style trailers.
* If you use cheap and quick 3D models based on 2D characters... well just don't. Nothing looks worse than bad 3D trying to look like good 2D. It'd be better to use bad 2D in it's place, at least bad 2D retains it's charm - bad 3D is just helpless. It's like the difference between those real puppet grandparents, and those CGI grandparents in the Wonga adverts. One is awesome, the other makes me ashamed to tell people work with computers... It's really like they drained the life right out of those puppets, and that's how I feel about bad 3D models of good, traditional characters

. Hope you get what I'm on about with this.... been a long day.

I am the one who knocks...
