Make sure that the light conditions are good and you have placed ample artificial lightening in case it is needed. Pictures usually come out bad if the lighting is insufficient.
Make sure that the pictures are in focus and there is no blurriness in them. Blurred pictures are useless for stock photos and will be waste of your efforts.
Good Quality Camera
You have to use a decent quality camera to ensure decent results that will be acceptable as stock photos. It is also not a bad idea to have the settings for the sharpest results which will add a lot more clarity to the pictures.
It is not a bad idea to take multiple shots since you can never be certain that a lone shot will come out perfectly. Take two to three pictures every time and take a quick look to make sure that they are coming out well. Using a digital camera, one gets a chance to see how the pictures are coming out with little effort.
Use Your Imagination
Try to take pictures from conventional as well as non-conventional angles. Sometimes taking pictures from different style can strike a chord with the user and it can help you finding a greater demand for your stock photos.
Use Real Professionals
For giving the photos an authentic look, it is not a bad idea to get real professionals in your pictures. If you are taking pictures of a construction worker, a doctor or anyone else, try to find actual people from these fields. The pictures will come out really well.
Get Photos Copy Righted
You need to copy right your images to protect your work. You may need the written consent from the models first but once you do that, get them copy righted in your name so that no one can use your pictures without permission. It can help you earn a little bit more to add to your day job.