Once you finish your script and you've had it looked at by other people, you start getting into pre-production. Pre-production is a pretty big topic, you are, to put it simply, preparing for production, the shoot. As a film maker, especially in the beginning, with short films, in a project of your own, its your job to get all the elements together and organise them.
There isn't any real order that this should be done, a lot of the time you'll have a bunch of things going at once. which is good. The trick is to get everything together for the shoot date.
What you become in the pre-production process is a producer, you manage people and spend a lot of time emailing and calling. If your budget is low, which is most of the time, you're also looking for like minded people. Get those involved that can see that your project will benefit them. Work with enthusiastic actors, proactive editors and cinematographers. People who you know want to be in the game just as much as you do.
If you don't have these types of people your project will suffer and it's only frustrating for everyone involved. Many of the types of people you'll need are:
Actors. Some of the time it's tempting to just get your friend or someone you know who did drama class in high school, or even yourself to play your roles. This can work, and sometimes is fine, but there people out there who have done acting classes for years and who have probably spent a great deal of time, effort and, not to mention, money doing those classes. Actors can make or brake your film, I'm sure you've seen it in other films. There are plenty of sites that will help you source actors, find them and use them. And most important of all, before you shoot rehearse with them!
Editor. Often a film maker can edit, you learn to cut video at high school, at home and then again at uni if that's the path you chose. But consider what a fresh eye will bring to the final cut. Also consider that as it's your 'baby' you'll want every scene, almost every take left in. An external editor will see a project completely different and possibly, if they know what they're doing, (of course they do, other wise you wouldn't have asked them) will give your scene continuity and depth, they'll really link it together without wanting that obscure shot that you love but, just doesn't work.
Cinematographer: Again, you can do this yourself, but film is about collaborating. A DOP will be able to talk about shots, framing and the right equipment to use. They could possibly think of something or a way of shooting something that you haven't thought of. Also if you don't have to be behind the camera, making sure the camera is recording, you can focus on performance and directing.
Director: Of course, you may not be a director, directing is a skill in itself, just like the other roles. If you want to just write and produce a good director will have good vision and scope for your project. They will be able to connect with the actors and understand where they need to come from to get into the role you've written. They'll also know what the cinematographer is talking about when they role off a bunch of equipment that they have or need.
Writer: As has been mentioned in the previous posts, you may have an idea but no way of writing or any idea about how to get it into the proper format. Writers are around and they can cost money or they can just be interested in getting involved. It's about finding someone proactive, someone, hopefully with a sample to show you, that will deliver, on time.
Producer. Another producer on your side is an enormous help, if you can divide your job and get someone else to organise things it makes your life easier. Even if its just organising rehearsal times, then you're able to focus on getting the right location. Location it almost a person in itself. The right location can give your film another character that most people won't even realise is playing a part. A producer can help in many ways and sometimes this person can be the director or cinematographer. Whoever it is treat them well.
Sound. An extremely important part of all films, including silent ones, is the sound. If it sounds bad, it looks bad. If you can get a dedicated sound guy to do your sound, get them! If they can do post as well, even better! Production sound and post production sound are very important, this can't be stressed enough.
It's a long post this time, a lot to cover. Yet the surface on this topic has really only been skimmed. Pre-production is sometimes longer than Post production, as you rely on other people to get back to you or to let you know somethings available on the right dates, you can be waiting a while and then you keep others waiting and it goes back and forth. But remember to keep everybody in the loop, let everyone know about any changes or updates. And of course have fun in the process.