Kinda basic stuff this, but who cares?
Always put a line of text on its own layer, makes it easier to edit out and fix until PDN gets better text handling.
When compressing a file with the jpg format, always compare your setting to 100, not 99, not 95, not 90, 100. so you can see the exact different between 70q and 100q.
Always learn to use more "advanced" options such as twist and rotate, alpha masking and curves. Some are ridiculously easy to learn.
Its better to move an image with the mouse, rather than the arrow keys, if you move that image 150 times, then decide to undo the whole thing, you'll have 150 steps of moving to wait through.
Know a plugins limits, some like Gentree and other graphic generators can easily crash your computer if you put the settings too high.
Always make a picture larger than you need it, its easier to resize 500 to 350 than to size 250 to 350.
Experiment with generators, gradients and layer options. You'll always get something nice.