For national funding there exist often official detailed guidelines about expected/prescribed length, style, content, outline of the application. You probably also find inofficial guidelines on single university servers by googling (filetype:pdf, inurl:edu)
Very similar rules of thumb as for writing a paper and getting it through the review process apply: No redundancy, logical consistency, clear structure...
And like publishing papers you learn it by doing. If you never wrote a paper and try now to write your first one and submit it to nature/science, reading a former nature/science article even about research of your field will not help you a lot. In the best case someone who reviewed for that journal takes a look on your paper, which is often the professor.
The big difference to writing papers is the section about your financial/working plan. How much money do you need and for what. This needs advise from experienced PI's, otherwise you might even in the case of funding end with much less than you need to successfully conduct the project, as often only a fraction of the requested money is granted.
Contrary to a journal review, the examiners scrutinizing your application are often no real experts in your field of research, as the pool of reviewers for national funding is much smaller. Therefore, the level of comprehension of the examiner will not be as high as compared to a journal reviewer and you have to write your aplication accordingly. Depending on the goal of your project (fundamental research, prototype -> TRL level), more scientific/technical/economic reseasoning and planning is necessary.
If you have experience in writing papers, I don't think reading old applications will help you a lot and improve your application significantly, as the application guidelines often set so much constrictions to describe your project in the necessary shortness. And if not, I think you might waste a lot of time without an experienced reviewer of your application.
I would also rather suggest to you to take courses on project managment at your university. In the end not the better scientific idea gets the grant, but the project that seems to be well planned and has all obstacles and details foreseen and listed with an according project/financial plan.