Slightly blurry pictures with canon xsi
I have a canon rebel xsi and am having some issues. I'm not sure at all what is going on but here's the deal. I've had it since may and taken some really super shots. The past month or two when I take pictures they are slightly blurry. Maybe one out of every 20 will be as crisp and clear as it should be. I have used auto focus and manual focus while taking many pictures of the same stationary subject trying to figure out what's wrong. I'm sure it's either something very simple that I'm doing but can't seem to figure it out myself. Any suggestions and help would be great! Thanks so much.