Don't skimp on the shiny bits, faucets, knobs, etc. Use classic styled fixtures with clean lines but that don't have a huge price tag. Go to Goodwill, Salvation Army, Tag Sales, etc and find good, well made furniture to decorate with. Make sure you always have multiple sources of light, work in compositions of odd numbers, install dimmers on every switch, keep surfaces clean, use common materials in creative ways, and always check on websites like Overstock.com for bargains.
Also, COLOR! Don't get stuck using only neutral tones. Mix in some good Primary Colors to add punch to your designs.