My big tip for macro photography with a DSLR (unless you have a macro lens) is ZOOM IN. You cannot focus very close to the flower, so zoom in. I used this technique in all three photos. Also, don't be afraid to use manual focus sometimes.
This was one of the first pictures I took with my new Canon EOS Rebel XS. It has brilliant depth of field, even though I used the kit lens and have not yet purchased a macro lens.