1. Photoshop is just plain intimidating for a lot of photographers, but if it can be a lot easier to master Photoshop if you approach it as a toolbox packed full of every tool you can imagine. If you try and use all those tools at once you're gong to end up in a giant mess. But if you take it a bit slower and master each tool as you need it, you'll not only find it easier, you'll remember what you learn for next time.
2. When trying to do something, see if there's a plug-in that does it for you. There are a lot of things you might want to do with Photoshop, but it would mean tinkering with values and brushes for hours. But sometimes other people wanted to do the exact same thing - in fact several people did, and they created plug-ins and brushes, which they offer for free.
3. Sometimes the best digital fix of the mall is a Depth Of Field adjustment. If you find there's something in a frame distracting from your main subject don't despair. There's some easy Depth-Of-Field actions you can download (search Google) and fix those images in a flash. No need to spend a fortune on a f1.2 lens... do it in Photoshop instead!
4. Anytime you find yourself stuck needing to use a weak image, consider turning it into black and white! Sometimes we miss the shot... that's life.... but if that weak image is one that would really complete your set, consider turning it into black and white or sepia. The change will often disguise contrast or brightness issues, and make your corrections harder to spot.
5. Always keep the raw layers on your adjusted files. It might seem like overkill once you have the perfect image, but saving the detailed layer files as well as the output is smart. You never know what a Client might ask for, and there is nothing more frustrating that retracing your steps and trying to remember what settings you used, when all you really needed to do was make some minor change to once layer.