Learn your short-cut keys!! It makes life so much quicker and easier... It means you don't have to select the tools all the time
For example here are a few that I use often...
CTRL + Backspace or ALT + Backspace : fill a selected area with the foreground or background colour.
CTRL + A : Select all with the marquee tool
CTRL + D : Deslect your selection
CTRL + U : Bring up the Hue/Saturation/Lightness window
Secondly use layers! And learn how to use them properly! They are a great feature. I don't know how I managed to make graphics when I was using Corel Photopaint without layers. I fyou keep the different colours on different layers then you can change things very easily.
Instead of using the eraser tool put on a layer mask. Use the paint tool to paint out the parts you want to erase... then if you change your mind later you can add bits back in by changing the layer mask again. You can get some great effects with masks and filters if you play around a bit!
Do you have a black and white image that you'd like to make coloured? If you remove the white background you can paint under the black outline and end up with some very professional coloured images. Here's how you do it...
Make sure that your colours are vibrant. Use the Brightness/Contrast window to make the white true white and the black a nice inky black. Now go to the Channels pallete and click the button at the bottom that says 'create new channel'... now you've selected all the white!! Press delete to get rid of it.
Now go back to the layers pallette and select the 'preserve transparency' option. Now select all and fill the entire image with black. This will make your lines darker again.
Now use different layers for each colour you want to add. Keep adding colours underneath the black layer until you are finished. If you want darker outlines try just duplicating the black outline layer.
This is a great technique to remember
I use it a lot.
Thats all from me for now...