I don't mean to sound patronizing, but the beauty of stock photography, is that it is everywhere!
Wherever you go and whatever you do, look around you. This time, don't just look at the photographs from an onlookers point of view, look from a photographers (a stock photographers) point of view.
Check out what kind of photos are being used and what they are advertising. The chances are that a high percentage of them were bought from stock libraries. Think about what kind of photo would sell, or help to sell various products.
Ok! I get the message, but where can I start?
Well, why not have a bit of a play. Think of a theme, like food (food is a massive demand item for stock photography and has been greatly covered) and go and buy some. Narrow it down to say bread, and buy a rustic loaf of bread, a block of cheddar cheese, a jar of branded pickle and a block of butter. Add some things like a nice bread knife, lettuce, fresh tomatoes with a spray of water on, wooden bread board...are you getting the idea?
Stay on the rustic theme and arrange the lighting to look like morning light beaming through a kitchen window (Use a template to shine the light through maybe). Experiment with the light and maybe spray air freshener or boil the kettle to create a misty effect, maybe a vase of fresh flowers in the background...I can see it now! This photo could be used for a pickle ad, or butter, or bread, or cheese ...
My point is that once you start to think, the ideas for stock photography are endless, which is a good thing because to actually make a living from stock photography, you are going to need a lot of photographs.
Because there are so many people competing, make sure to read up on key-wording your photos when you have submitted them. There's no point in having 10,000 photos online if no-one can find them!
Set up a small makeshift studio somewhere in your house, permanently if possible, that way you are ready when the still life ideas start coming.
Take your camera with you everywhere, take photos of whatever catches your eye. Go through your current library of images (if you have any) and see if any could be used. Run them through a photo editor if necessary, to get them up to scratch.
Visit a couple of stock libraries online and see what they have on their books, don't copy or plagiarize them, but use them to create ideas of your own.
Always carry a bunch of model release forms with you. You will need a signed release form from the people in the photos if they are to be used as stock photography, particularly in advertising campaigns. If you take photographs of buildings, get a model release from the owner for that too! Sounds strange, but the owner of an idyllic looking cottage you would like to use on a biscuit tin, may not want his home on all the coffee tables throughout the country.
Read the rules that are available through all reputable stock agencies before you start, and then go out and get 'em!
Don't be disappointed if your work doesn't sell immediately, or a few of your images are rejected because like anything, stock photography is a learning process. With a bit of hard work and perseverance it is possible to make a career from it, just get clicking!