It's been brought to my attention (it seems) that when one is making a teaser trailer, one needs to think about 5 things;

Budget; Pretty straightforward if I do say myself as everything costs, why should a trailer be any different? Have you got the money to endorse a trailer for a well-known blockbuster? Or maybe, considering your budget, you'll want to go for something a little more... affordable. Namely cheap, small budget films. Whatever your reason/target, know- that it'll cost ya!

Actor/Director; Usually when trying to get your target audience interested, trailers tend to have the names of the directors and/or actors involved in the Teaser. Most will know this technique as the 'star system'. Fans of a particular actor/directors work will blindly go to see and anything they release as they are an existing audience. This knowledge plays into a producers hands easily.

Sequel; Was there a previous film that is widely popular? If so then in retro-spect, a trailer isn't and is needed. It's needed to advertise to its fans that the sequel will be coming out. It's not needed, however cause the audience who liked the previous film will know what to expect and will show up at cinemas everywhere regardelss of a trailer.

Adaptation; This can include anything from books to games, media to non-media. It could really be anything one sets their mind on as long as there is already an existing product. Even TV can be taken into account on this subject.

Action/Adventure; These kinds of teaser trailers are in their own category. Namely because this genre begs for the largest budgets and biggest special effects out of all the genre's. This could easily be a problem for small companies who would regard this a huge risk.

2012 Teaser and Official comparison

There is a noticable difference between both 2012 trailers. The teaser's intention is to grip the audience and keep them interested- wanting more. The official trailer gives the audience a sneak peak at what will be in the actual movie. Chances are, if you liked the trailer, you'll love the movie. The official trailer features a voice-over and longer clips of the movie which gives the audience a stronger sense of what the end result of the film will be than the teaser, which contrastingly shows very little footage of the actual movie and is usually moved along by mysterious text that forces the viewers to think a bit. The music/sound seems to be far more dramatic in the teaser trailer than in the official trailer. The purpose if this is to draw the audience in, making the official trailer seem more effective due to it being more accurate and less dramatic, which is not the point of the offical trailer.

2012 Teaser Trailer

Halo Teaser Trailer Analysis (Add-on)

Because this trailer/movie is derived straight from a popular video game, an audience already exists. This means that once the widely known Halo logo is shown, fans will instantly understand what the film is about. The hand-held camera technique makes the audience feel apart of the action and the fast-cutting keeps the audience alert and interested. The whole film is based around/from the game, therefore it makes sense that most elements from the game are incorporated into the film.