In my "job," I help people find the resources they need to start their business.
While I can point them to many resources, online and in real life, the single best piece of advice is perhaps the most common sense.
You can look at business plan templates at the library or wherever you can find them. There are PLENTY of great resources; I know, I work with many of them. This is not to suggest that you should talk to a SCORE representative, your local small business development center, or even a Chamber representative. You should.
But perhaps first and foremost, talk to someone who does what you want to do.
I'm sure others have said it, but it ALWAYS bears repeating. Find someone who does what you think you want to do and ask them questions.
Don't confuse this with finding a mentor. A mentor can be from ANY business, in fact, the best ones are probably NOT in the area you are in to give you the fresh perspective you will not find from someone who does what you want to do. They will be around for the long haul. Poking at your plans, nitpicking, and giving advice that you would not get from the peer.
Peers in your field are going to be able to tell you like it is! And if you can't find one near you (as I would suspect you might no be able to find), look all over! My best example came from a client who was looking at starting a VERY unique business in the area. There were no others like them. I suggested that they talked to a similar business several hours away- just call and ask!
What's the worst that could happen if you ask to pick their brain? They clam up? Find another!
Eventually, someone will be willing, as most people are to talk about what they do and how you could learn from them!
Heck, that's what I do every DAY.