Look upon grant writing as the rigorous intellectual challenge that it is. You can learn an amazing amount in preparing a good grant application, and that learning can not only help get you funded, but also help you do better work once you are funded. They should be the first sections you write, because it is always good to outline what you plan to do before beginning your detailed writing. They should also be the last sections you revise, because it is imperative that they agree with what you have written in the Experimental Design and Methods section. Indicate how the results of the various proposed experiments will mesh to form a cohesive whole that will advance significantly your field of research.
Most good research is hypothesis-driven.
Design experiments that will test various predictions of your hypotheses from multiple angles. Include only experiments that you have the expertise to do, and for which you have some preliminary data demonstrating feasibility. The Background section should convince the reader that you have a good command of the current research literature in your field, and that you can be objective and thoughtful in your analysis of data. You need to convince the reviewer that you are planning to test hypotheses, not simply to collect data to confirm your favorite hypotheses, and that you are open-minded enough to reject your hypotheses if the experimental results so indicate. Make certain that your background discussion remains focussed on the issues your experiments will address.