You can't make money with Photoshop if you can't use it well. I've made a list of a few Photoshop tips for making professional-looking designs.
Don't use the smudge tool, or if you use it, don't use it much. When used properly it can be very effective, but usually it just makes things look messy.
Make sure everything looks sharp. Don't over-sharpen things to the point that they look low quality, but make sure nothing looks blurry. There's nothing more unprofessional than blurry artwork.
Use a color scheme that matches. Shades of blue, orange, and white or black look much more effective and professional than bright red, aqua blue and bright green. Make sure your color scheme always matches properly. You can use Color Schemer to generate color schemes.
Make sure everything looks nice and simple. This doesn't mean you have to do minimalistic designs, it just means you shouldn't crowd your designs with a whole lot of useless parts that make the overall design look messy. Sometimes the easy way is the best way.'
- Be creative! Don't be afraid to try new things. Try to make your designs look unique and appealing.
Happy Photoshopping! :)