To get started just write down your creative ideas. This could be just a paragraph to a full script.

Some points to consider for short films are:

Having a concrete plot:

Put yourself in the audiences shoes and ask yourself, do you connect with the plot?

If the answer is no, chances are that your audience will not either.

For the practical side you should consider budget constraints. Having a written budget in the form of an Excel spreadsheet or professional software, you'll be able to allocate your funds efficiently.

Without planning the financial aspect, your film could be over-budgeted and may not get finished.

Getting clearance consents:

All the actors, editors, music directors and other crew members, should sign a clearance form for the film. Speak to a lawyer in the industry for tips.

Trying to get these signed after the completion of the shoot can be next to impossible, so get them signed before hand.

Cast actors that suit the role:

Casting is difficult on small budget short movies as you may only be able to afford your friends or family who work for free but have no acting skills.

If you approach acting schools, you may find some students who are willing to work just for recognition.

You should at least have a good looking pamplet made, advertising your project to draw some interest.

If you can afford a professional actor you will have someone who may portray the character you envision with the most accuracy.

Put some money on sound:

Bad quality sound effects often makes even a good short film bad to watch. Either beg, borrow or steal a boom mike, or a wireless mike, and your film will be appreciated more by the target audience.

Fix it now, rather than in post-production:

Most of the fixes on errors done at the post-production stage don't appear very good and consume a lot of time. If there has been an error in recording, shooting, framing, etc. a scene, makes sure you rectify the mistake as soon as possible if possible.

Never zoom in a shot:

Zooming is a not a good idea for a short film, unless done by a professional photographer. Using the glider of the camera, a dolly or a cut would be a better option to concentrate on a particular object rather than zooming.

Know the clich's of movies:

Many often repeated clich's in short films include the use of dream sequences, or waking up from a dream acting alarmed.

Avoid shooting outdoors at night:

Shooting outdoors at night requires good lighting knowledge to get quality footage. If you don't have experience, try to avoid night shoots by rewriting your script.

If you are experienced then go ahead but spend some money on good lighting and position your actors so they maximize on limited light. Cameras have difficulty getting quality images in low light.

Ideas may include:

Re-enacting History

War Shorts

Comedy

Musical/RAP

Documentary Shorts

Informational/Learning Shorts (How To)