Character They're exterior needs to clearly show their situation, values/personality, & other important things. Their interior needs to be shown through their surroundings and exterior to avoid excess exposition. When designing them you need to create a realistic and believable backstory and clearly understand how that has shaped their personality, values, situation. How do they react to events that cause excess of emotion in any direction? A character will react differently to things depending on their past experiences so they are important to have in mind when writing them, even if they are not necessarily needed for the film. A good idea of family, culture, and heritage also helps as this further shapes personality and identity. Identity (or lack of) is key to a character. Everything that has happened, is happening, and will happen will change them. Where they've been, where they are, and where they'll go also forms them. They must be kept in mind...
I’m going to write a screenplay for a short horror film. Currently I’m thinking of styling it like a found footage film, taking inspiration from ‘Digging up the Marrow’ which is favourite found footage film of mine. Although this is feature length, I’ve been looking at horror shorts on YouTube (mainly by CryptTV) with similar settings to see how the locations and stories have been adapted to fit the narrative of a short film. If I can find a location that suits what I want then I may make a short film but I think it will be unlikely so for the moment my plan is for a screenplay.