Grant writing is a career path in its own right. It's tedious and involves a ton of research and throwing lots of ones own time and effort against a wall and seeing what sticks.
There are courses, and if I recall there may even be the odd degree offered in it (if you look hard enough). Being a grant writer, especially a seasoned and successful one (maintain metrics, even if they're your own), pays off huge!
I did this for a time for a charity I did volunteer work for. This is a great approach because once you've put forth a good faith effort, you get to keep the files you had access to ... AND basically received training for free. If you do a couple months like that at 2 or 3 different NFPs for a couple years you've immediately catapulted to inheriting [a] one of the most muscular databases ever (presuming you're synthesizing them all into one of your own), and [2] some awesome training, insofar as it may be basic training (ultimately, it's fairly basic stuff anyway) but it's from a half dozen different perspectives (and the additional perspectives is mighty valuable). Naturally, you do this ethically, do your best for these folks and you don't take what you ought not. BUT, think of the advantage!!! Now THAT'S volunteerism with a payoff!