Assuming your camera allows some sort of manual control:
- Use a narrow aperture e.g. f/22
- Shoot a light even background e.g. blue sky or white sheet of paper
- May need to, say, +1 EV if shooting white sheet of paper to ensure proper exposure
- Manually set the camera out of focus
- Slightly shake the camera while exposure in progress, usually a few seconds
- Examine using camera LCD, magnifying the image to see the dust
Alternatively you can also load the image into software like Adobe Lightroom and examine from there. Lightroom 5 has a feature called Visualize Spots which is very handy to identify sensor dust, and subsequently clone them out.