Digital Doodling Techniques - All You Need is a Scanner

1. Choose a reasonably thick felt-tip pen (Zig Writers .05 nib are good) and go forth and doodle on plain white paper. (The good thing about this technique? - 1. if you’re not happy, just screw it up and chuck it at your family or 2. Even better - get your children to do it for you - they’re natural doodlers with no inhibitions)
2. Scan your doodle in at high resolution for detail.
3. Open the scan into your digital software / photo editor.
4. Clean up the scan - normally most photo editors now-adays have a one-step Fix Photo option which will generally intensify the contrast. If this doesn’t work, use the manual contrast and brightness buttons to intensify the image as much as possible so that you have a nice bright white around the doodle.
5. If you haven’t already, set the background image to a layer image - normally this is simply selecting the image in the layer palette (you’ll only have one layer), right-clicking and choosing the "Promote Background" option.
6. Choose your magic wand selection tool, and click on the white around the doodle - this should select all of the white of the paper background. If not, play around with your tolerance settings for the magic wand tool - these should be in the tool bars above your editing windows.
7. If you have any white bits inside your doodle, press your control button plus click on these with the magic wand still selected.
8. Once you have all the white selected with the dancing ants selection lines, hit the delete button. Select—>None to get rid of your selection lines, and the doodle will now be surrounded by transparency (normally checkered background). Crop the doodle, then save as a .png file. You can now use this to overlay on any of your digital projects.
   

Some permutations

1. Instead of deleting the white background to make a .png file of your doodle, leave the white background and create the doodle as a brush file. This involves exporting as a brush from your file menu. Create a whole collection of doodle brushes and export as a brush set.
2. Whilst you still have the white paper background, use your magic wand tool to select internal white areas (play around with your tolerance tools to ensure you only select that area you want) and use the Paint Bucket tool to fill this selection area with a colour chosen from your colour mixer. (Or even a gradiant). This is how you colour things like butterflies etc.
3. Once you have the png file itself (normally in basic black), use the Magic Wand tool again to select this black (tolerance normally very low). Then use the Paint Bucket to fill this selection with colour - change black to yellow or red for instance.  Sometimes this thickens the outline a little, so be careful about how you select using the magic wand selection tool in the first place. Play around with things like feathering, and other tool options to ensure you select as close as possible to the edge of the black.