Here's a few general tips, and I'm not sure how helpful they'd be:
stock images cropped creatively make great bases. WeHeartIt and DeviantArt are my two favorite places.
fonts are your friend. dafont.com is a nice repository of free and easy-to-use fonts. A pretty font makes stock images more attractive.
Lastly, once you've decided on the font, use your layer transparency and/or look. Hue, Saturation, Hard/Soft light, Overlay, and Burn are the ones I've found work best. You can duplicate the text layer, and use it to create a shadow, or a border.