Getting from researching and thinking about initial ideas to a well conceived, written proposal is going to take work. Helpful tips might be to draw the concept - as a spidergram/mind map or record your thoughts on a dictaphone. This will help to flesh-out ideas, and articulate them in a way that is external to you. Pushing your ideas through such processes helps to clarify them and hone them into a form which may be easier to communicate.
Do not be afraid to use simple language, but you can write in a style that uses industry language (arts language). Language should be natural to you and the concept you are communicating. You can write in a way that expresses creatively your ideas and resonates with concepts and you may find you write best when your personality can come through. Remember who will be reading it and make sure it is comprehensible - there may be people there who are not be as specialist as you.
Keeping references, footnotes, and appendices for dense, complex, and theoretical information keeps the 'weight' of the document without slowing down a more general understanding.
Greystones Educate Together National School appointed a voluntary committee with relevant expertise to oversee the per cent for art commissioning process. An external curator, Máire Davey, was appointed specifically for her expertise in working in a highly collaborative way as meaningful involvement from the students and school was viewed as central to the process. The procurement route chosen was limited invited competition.