To create a trailer for a retro/ b-movie, I think is crucial to understand what cinematic language is usually used in a B-Movie. As mentioned before, technically a B-movie is typically a low budget type of film, that often used genres such as suspense, horror, sci-fi, western, exploitation or gangster.
Researching in-depth this definition, I have to also mention that they often were cheesy, with silly looking creatures, featuring some of the cheesiest and silly acting and dialogue seen in film. Thus, B-movies have a style of their own.
All this factors may give a bad reputation to B-movies, however, these factors are actually what makes this type of films memorable and part of Cinema Culture. In this period, the directors took small budgets and made some of the more memorable sci-fi/ horror films known to date, why?... because although they didn't have good acting, nor great special effects, nor great storylines, They played with the the spectators imaginations and usually demonstrated most of the child-like innocent desires coming to life.
To summarize, Directors had to make the most of a movie by using micro-budgets, they often added cheap special effects, bad acting, weird storylines, and voiceovers over the acting, often used as the narrator of the story, but they made the spectator's imaginations work .