I started writing proposals while in a smaller company. We had a requirement for new products and I just took the initiative and wrote the proposal. Of course by that time I had already written, Statements of Work (SOW), testing procedures, equipment details, software instructions etc. I have also taught classes in a technical school, so have also written lesson plans. So I think that my background and experience in writing may be a bit more detailed that many others. I know that you had better have a very good background in Microsoft word, and English composition. You need to know the basics before doing a proposal.