One of the things that any new graduate student will have to do is write a research proposal. You may have to do this for admission, or for grants. Unfortunately, most new students do not know what a research proposal should be. I had this same problem when I started. At this point I have a slightly better idea about what makes a good research proposal, although I am no expert. Hopefully, if you need to write a proposal, these will help you figure it out.
A proposal is supposed to be a description of your goals for your research. It should not be specific on exactly what you will do. After all, if you know the answers already, it isn't research. A proposal should describe your questions, and why they are important questions. One exercise that can be helpful to figure out what questions you should ask is to imagine that you are a director of a fantasy computer science research lab, and you must decide what projects to fund. To find some interesting directions, it can be very useful to see what others have in their research plans. For example, DARPA's research project list is a good starting point, as is an outline of any professor's research. Try to think about what will be needed in at least five years. Anything less than that probably better suited for a venture capital funded start-up business plan, not a research proposal.
It is very important that you read a couple of the most important papers in your field before writing your proposal. Since it is a proposal, you do not need to read too many, but you probably want to read at least two. These papers will give you an idea of what other people are doing, and where the field is headed. You want to propose research on something that no one else is doing. Google Scholar is a good way to evaluate which papers to read, since it will tell you how many other papers cite a particular paper. Generally, you want to read papers that have been published in last few years, have been cited by others, and/or have been published in the top conferences or journals.
In your proposal, describe an angle on a problem that you think is important, and doesn't seem to be covered by the papers you have read. For academic research to be considered relevant, it has to be new and novel, so anything that others are working on would not be a good choice. It is very useful if you can convince someone who is working in the field, such as a professor or a graduate student, to read your proposal. In order to facilitate this, be sure to start your proposal early so they have lots of time to read it and get back to you before the deadline.