Provide whatever information the reader will need to be persuaded, and no more. Third, describe how you will evaluate whether or not your solution solves the problem. Most sources require an extensive evaluation section. Evaluations can be formal or informal, formative or summative, internal or external, depending on the project and the funding source. Make sure that your system of evaluation will, in fact, demonstrate that the need described in the first part was addressed by the solution you propose in the second.
Many reviewers look at the budget first, before they read the narrative.
They assume that the budget shows what the proposal is all about in just a few pages. The various items in the budget should follow the same order as the activities you propose in the narrative. The Grants Office can help you prepare your budget, can tell you the correct fringe benefit and indirect cost rates, and can check your math. There should be a clear, easily discernible relationship between these four parts. The problem section should focus on a particular need, the solution section should outline a specific series of activities which will address that need, the evaluation section should outline a method of evaluating how the solution met the problem, and the budget should show how much each element of the solution will cost and where the money will come from.