If you improve your scientific/technical/research writing, then you are able to write good project proposals. Please find attached the brief booklet on scientific writing. I guess it will be useful for you.
I found the following (free) online course from Stanford very helpful. The professor is in medical research, but the majority of the tips she gives are applicable across fields.
After having completed the Research and possessing a pile of information, data, literature, questionnaire and responses, analyzed tables and statistical information... the final stage is to prepare the report....
The Art of report writing depends on the picture or vision on the intend... Once the frame work gets into place then working around it and making it customized as per the audience to it can be carried out...For example, i am sharing one of my own styles ... on a paper called "Employ ability Skills" ... first a one page report (as enclosed...
Journal work (editing, reviewing), and reading or reviewing grants greatly improved my own writing. Primarily, it exposed me to a variety of conventions for presenting and sharing information, giving me more tools at my disposal.
In terms of writing good proposals one of the best things you can do is use a template. See the link for the World Health Organisation's template for a research protocol.
See attached. These come from my well-reviewed book 'Study Skills for International Postgraduate Students (Palgrave, 2011) -- currently being translated into Arabic.
The best method to improve your technical writing skills and write good proposals is practice, practice, practice. Working closely with a supervisor or mentor and watching how they write, assisting in writing their proposals, asking lots of questions (an apprenticeship model) also helps greatly. Although templates work for some people they don't work for everyone.
My two cents in addition to the other great answers: regarding specifically the *grant* proposals, see inter alia the book and the site "Four Steps to Funding" ( http://fourstepstofunding.com/ ); some further links are here : http://aclinks.wordpress.com/2009/03/10/how-to-write-grant-proposals/
'The Research Whisperer' is an advice-packed blog from a research funding guru, and this post on budget planning highlights an important aspect of any project proposal: