Myths and Legends can provide some much needed inspiration, especially if what you are writing comes under the genre of fantasy (plus some of them can make an extremely amusing read!). Myths and Legends can also provide inspiration, not just for the characters, but also for religious beliefs that your characters may have, as well as giving you ideas for strange and wonderful creatures and monsters that you may dream up. Reading up on how people viewed certain and animals can also add to your book a certain depth, as it can give a place to work from when you come to add symbolism to your book. You will be able to find books of legends, myths and fairy tales in your local library or in book shops.
For anyone interested in history, you have a great wealth of inspiration right on your door step. Historical Romances, even though they do tend to include romance as the name suggests, you can also cram in tons of action and adventure as you like (but try to keep it believable), and you can use real people, and you can't get done for plagarism, which is always a good thing. Histrory can also be used in subtle ways, as you can suggest at real historical places or happenings without actually stating what you are really refearing to (again another plus if your writing fantacy). If you decide to base certain places in you book on a real places and area that you know, try and make up your own names for them, as you don't want your reader to get confused with the real places.
Even using people that you know as the basis for some or all of your characters, can be a good idea, but you might have to watch them for quirks and unique characteristics that you could use for the characters, just to give them that extra edge. Using people that you know for the basic of your characters, means that you don'e have to spend as much time making up completly new characters, as you have all the characteristics that you need close at hand. Even looking for little quirks in strangers while your on the bus or train can give you ideas (but don't let them know that your watching them, just to be safe!)
Talk to people! Fpr example, there are professional organisations for almost every trade. You could try to contact one of them and ask if they can provide a little insight as to the details behind their trade. A little bit of authentic information can go a long way to bring a story to life. I had a friend write a novel based on the Titanic, but from the point of view of those left behind. She managed to contact the surviving relatives and had some very interesting phone conversations as a result!
Task
Try and keep a note pad with you, because you never know when an idea might stirke you.
Go 'people watching'. This can give you great ideas for little intersting quirks a character might have.
Visit the library and read books on your chosen subject
Try and keep a note of how a certain scene, like a sunset (yes, I know it's cheesy), or a storm, can produce certain feeling, and effects the surrounding landscape. This can be used to produce certain emotions with your readers, as well as being used for symbolism.
