First of all, you're going to need to define the scope of the project, which is a huge part of project management jobs. Basically, what are you trying to get done? It's easy to become sidetracked, especially if there is a client demanding more, but by defining the scope you can make sure that you don't go outside the original parameters of the project. It might seem okay to do a little extra here and there, but keep in mind that this can cause harm to the project if you're not careful. It could even result in you not finishing it!
What type of resources do you have at your disposal? Determining this will determine how exactly you will completely project. You will need to assign a budget to every single aspect of the project, but you've probably guessed that resources don't always amount to money. You also have to deal with people and equipment, and these needs to be allocated appropriately.
In a project manager job, you're going to need to determine how long the project will take, versus when it is scheduled to be completed. If you are lucky, then these two time lines will coincide. If you are unlucky, then you're going to need to find a way to MAKE them coincide.
Now that you know what you're going to do and how long it's going to take, it would be a good time to get your team together. The project manager jobs involve communication, and lots of it. Normally you will not pick your team, they will have been assigned by their supervisor, and you need to assess their strengths, weaknesses, and get them to work on the project.
In doing this, project management jobs require that you put a plan together. Determine how, when, and why you're going to perform each step. The planning part might not be as exciting as actually working on the project, but it is a necessary step for all projects if they are to succeed.
Make sure that you keep documentation on each and every part of the project. Project manager careers require a lot of writing, so make sure that you're ready for that. This is mostly so that others will be able to look at your notes and determine how something was done. It will also help you along the way, so if something went wrong you can go back in your notes and find out where the plan went awry.
It takes more than just you to make your project manager job a success, even if you are a huge part of the whole thing. You will need to rely on your team, their input, and their experience. You can't do it all yourself, so get all the help you can to better yourself and your project.