JUSTCREATIVE - THE PROCESS, AND A SAMPLE TEMPLATE TO EXPERIMENT WITH
This designer includes images you can work with to follow his instructions, and he guides you the design process - including drafting, getting audience feedback, and then re-drafting, making it clear what changes were made and why!
You too should be able to picture your final poster as a huge display in public!
VANDELAYDESIGN - 39 SPECIFIC GUIDES
There is a very wide range of step by step tutorials: sci-fi, 80s, 60s, Lord of the Rings, Indiana Jones ...
CLICK READ MORE below TO SEE MORE LINKS AND EXAMPLES
FILMMAKERiq - 101 SPECIFIC GUIDES!
These often home in on smaller elements, like how to replicate the Transformers title style, but includes a very wide range of guides, including comic book superhero, Disney, war ...
FILMSOURCING - MAKING A COMEDY POSTER
This one has a clear, simple guide on key design features of a comedy poster (from a professional who has created several real examples) as well as a basic template.
1STWEBDESIGNER - 140 TUTORIALS
Like several others, this is a mix of movie and other poster guides, but certainly includes some that could provide inspiration and a lot of help.
HEYPRINTS - 20 EASY TUTORIALS
I'll let you decide if his description of 'easy' is true!
The example below is an interesting one, not so much based on photography as using tools within Photoshop to construct an image.
There are lots more out there ... try searching for something specific: film poster photoshop guide minions for example, if thats what you were working on!