My husband mentioned the other day as he does every so often that he too has a story in his head but it has grown to be so large that he doesn't know where to start. After having him explain what he wants it to be about and who his main characters are I realized that he doesn't have a clue as to where to start. Then I realized that a lot of people have the exact same problem as he does.
The first piece of advice I gave him was to make a list of characters that are crucial in telling your story. If a character isn't needed or you could use another already established character to do or say what you want then cut the one you don't need out. Only keep what you need. If a character isn't useful then they really shouldn't be there.
Once you've paired down your character list then you should figure out if what you are wanting to say can be summed up in one book or should you break it up into a series. If you have a large group of characters with back stories that need to be told before you get to the juicy stuff so that the reader isn't lost then a series is your best option. A series will allow you to tell a large group of characters stories and cut some characters from your list if you still have some hanging on.
The next thing I like to do is I come up with a working title. It isn't always what I stick with but it does help steer where my story goes. A title is the most important thing when it comes to a story other than the writing its self. If the title doesn't grab the readers attention then it really is letting the story down. My rule of thumb is if I look at the title and think I wouldn't read it then it needs to be changed.
Another tip is to make an outline. I know that this is something that high school teachers tell students all of the time; but it actually works! An outline will help keep you focused if you aren't the type of writer who can just see where you left off and jump right in. It will also keep your story focused and keep it from getting all muddled up.
The most important advice that I gave my husband and I will give to you is to just have fun! If you yourself can't love and get lost in your story then chances are a reader won't be either. Put your soul into your writing no matter what genre you're in. If you aren't invested in it then just move on!
I hope my advice will help my husband or whoever stumbles upon this blog. I know that what I have said here really helps me when I have a huge idea but I'm not sure where to start. No matter if it helps or not I hope what someone really takes from this is that writing should be fun and take you on a ride that leaves you wanting more! Good luck!