One of the big differences between a DSLR and a digicam (assuming that's what you upgraded from) is the depth of field. This makes focus more important at the large apertures available for DSLR (even f/5.6 requires attention to the focus). Another big diference is Phase Detect autofocus systems, which is very different from the Contrast Detect autofocus on a digicam. I think the advice you've already gotten combined with more practice will help you greatly. Just keep at it and soon enough your shots will come out much better.