The wider the aperature the less depth of field([f2.8 vs f8]. This gives you a very sharp pic of your gun(or whatever), kinda blurs the background, giving the eyes more focus on the gun(or whatever). The 'auto' setting usually kind of sucks. With plenty of light, you should be able to set your cam on 'aperature' setting and control the exposure that way. You must, however, make sure your shutter speed is high enough to take care of your 'shakes', or use a tripod.
Usually also, the single flash on the camera really sucks. Either invest in multiple light sources or try to take your pics outside. The warmth of late afternoon really adds to pics.
As a general rule, the wider the aperature, the less the depth of field(the part of the pic that's in focus). The higher or faster the shutter speed, the more the effect of camera shake(or the movement of the subject) is minimized. Use multiple light sources and adjust positioning of them to create the shadow effect you're looking for.
Make sure that your focusing is precise. Bad focus blurs the results.
With a digital camera you can afford to experiment. Take a hundred shots at different settings and all you have invested is time(and battery life). Pick and choose from the results. Very different from the old film camera days when you had to pay for film and processing!
I'm surely not an expert, but just some observations(I think).
Iz