Sometimes, depending on the style of the dress, I switch out the self-tie belt with a separate belt that either matches or contrasts. I keep the belt that came with the dress because sometimes that look is better, but it is worth experimenting with other belts you may have.
And asfor tying the belts, I orefer a square knot on a structured dress and a full bow on most others. I've never felt quite right myself in a one-loop tie - maybe I'm not doing it right.