_cf gave me a few of these tips, and I added a lot of my own. Many of these tips are just basic know how, but they are definitely helpful. Especially for PS n00bs. x3
*Using pencil or inked art with a scanner, and a version of Adobe Photoshop
For keeping your line art separate from color, and colors seperate from one another:
Layers are your friends. By using layers you can not only leave the outline of your art untouched, but you can create separate layers for every aspect of your work, for quick, clean coloring and shading.
Start by creating a separate line-art layer~ MAKE SURE THE LAYERS WINDOW IS VISIBLE (In the menu bar go to Window>Layers. Make sure it's checked)
After scanning your pencil art, it will usually arrive in photoshop as the background layer. The first thing to do is to make a copy of the lineart into a layer: right-click the background at the layers tab, and choose duplicate layer. Name this layer as "line art".
Make the background invisible (click the eye at the layer tab) so that you're only seeing the line art layer. Click once on it to make sure that's selected.
Then it's generally a good idea to use the autolevels tool on the line art layer (shift+ctrl+L) to darken the pencil and whiten the paper.
To paint, set the blending mode of the line art layer to Multiply (look for a select box at the layers tab which currently reads "Normal" and change it to "Multiply"). Now create a new layer for the color (In the menu bar go to Layer>New>Layer (Shft+Ctrl+N)), and put it BELOW the line art (grab the color layer with the mouse and move it under the line art layer). Choose a color brush and paint on the color layer. You'll see that the line art will not be affected by the color brush, even as you cross it.
I recommend making a new layer each time you color a different part of the picture to avoid bleeding.
Eg: Keeping skin and clothes separate. Create a layer and name it Skin. Color all skin areas, and create a new layer, naming it clothes. You pull this layer so it's under both skin and line art layers (the layers at the top of the Layers window are the ones that appear on top) and color. You will see the skin areas you colored previously are untouched by your clothing colors if your brush strays over skin areas.
More tips on coloring:
*To quickly paint, you can still use the Magic Wand tool (In the tools window, it looks like a stick with a firework exploding out the end), choosing the "Use all layers" option (It's a check box under the menu bar when the Magic Wand tool is selected.) This tool selects all the area within closed lines. Careful that your pencil/ink lines all touch or else you might run into annoying issues with it, later. So, you select the area, and grab the brush tool, and color away inside the selected area till its completely colored. This is a lot faster than trying to do it with the brush tool alone.
*Remember to use the eraser tool to clean up any areas you messed up on.
*As long as the selected layer is one of the color layers, there will be no risk of messing with the line art as you select large areas to quickly paint them.
*The Eyedropper tool helps you quickly match colors you previously made if the color is somewhere on your picture. Just click the color area you want on the picture, and it selects that color for next time you use the brush, etc.
*Be aware of different brush styles and sizes. You can create softer looks with different brushed, and different effects with other brushes. Sizes are in a pretty much limitless variety for all your needs.
*When in brush modes you can change the Opacity or Flow of a brush by percentages. This can create transparent effects, or lighter shades of colors.
Eg: You want to use a transparent effect to make water look semi see-through. Pick a brush and a color and set te Opacity down to 50%. The line art and other colors will remain (if your layers are in the right order) semi transparent.
OR...you want to create a blushing effect, or even better, a pink/red spanked bottom. On the skin layer select a brush (with soft edges recommended, at an appropriate size) and select a bright shade of red. Then set the opacity down to maybe...25-20%. This creates a soft but not overwhelming shade of realistic pinkish red over the cheeks, whichever set you're coloring
(~Note the to create an even shade you must click only one and drag the brush--multiple clicks on the same spot will eventually lead to the actual color without transparency)
*Finding the color you want: In the Color Window, there are various view options to your preference. On the RGB sliders mode, you can quickly click a color area and pull the sliders to find a color in the right range, and fine tune it by double-clicking the box with the color in it. A new window appears with an even finer array of color options.
*Switching a scanned picture to RGB mode
In the Menu bar, click Image > Mode > and check RGB Color. This will open the picture to be colorable if it was in Grayscale mode. (Only black white and grays)
---> Shading and Lighting Tips:
Use the Lock transparent pixels tool (in the Layers window, beside Lock:, it appears as a checkered box) to lock the uncolored areas of a layer. This prevents you from coloring anywhere outside the already filled areas. With this, you can select a layer you want to add shading effects to (use the color window to find a darker or lighter shade and select an appropriate brush) and apply the darker/lighter color where needed. With the layer's transparent pixels locked, you can color easily on whichever layer you have selected without going outside of your already color filled areas. This is good for clean shading. Remember to unlock the layer when you're finished (failure to do so may cause errors later, eg: with the eraser tool).
--> *Saving Layered .psd images into JPEG or another Internet Friendly version:
In the Menu bar, click File > Save For Web...Alt+Shift+Ctrl+S [If you do not have Image Ready, this option may not be available depending on your PS version)
A new window appears with an actual size of your picture preview, all layers combined to be your final product. *HERE YOU CAN ALSO
RESIZE YOUR IMAGE TO THE SIZE YOU WANT!!!
On the right side of the window, select the image type (JPEG, GIF, etc...)
You can also change the quality percentile to make the space (eg: kb) your image takes up smaller. However the smaller the percent, the worse the picture looks. It all displays in the preview window.
TO RESIZE
In the Save For Web Window
On the right side of the window, where Color Table is the tab selected, select the second tab, "Image Size." Here you can change the pixel size and click "Apply" to preview the size. Make sure the "Constrain Proportions" check box is selected to avoid warping your picture. When you reach a satisfactory size, click Save at the top of the window on the right. It will then ask you where you want to save this new picture (~~Note that if you save as a GIF, JPEG, etc, it merges all layers together so that you can no longer open it and change it in Photoshop the way you did while layered. In case you want to change parts f the pictures, be sure to do regular the regular Save (Ctrl+S) option, making sure the file is saved as a .psd file.)
From the Menu Bar
In the menu bar, click Image > Image Size...(Ctrl+Alt+I)
In the new window that opens you can again change the pixel properties to change the size of your image. Use to magnifying glass tool to Zoom In and Zoom Out of the picture.
Finally,
Edit Undo is your friend. If you scribble all over your work in frustration then calm down again, you can Undo it either by clicking Edit >Undo (Most recent single step) / Edit > Step Backward (Multiple steps back)
Keyboard Shortcuts:
Undo (Ctrl+Z)
Step Backward (Alt+Ctrl+Z)
~Note that saving your work disables you from going to any steps you did before the save point, so careful.
Frequent saving is recommended, especially if your PC is prone to random freezes or crashes. It's one of the most disheartening things to pour hours into coloring a pic, and not saving it throughout the process at all, to lose all your work when Photoshop decides to be a betch and freeze. So, be wary.
Anyways that's all the basic tips and tricks I know, or atleast can think of at 2:30 in the morning. If you have questions about anything in this post PM me, or post it here, and I'll eventually respond one way or another.
Thanks and I hope it's helpful! If you have any Questions about trying to achieve a certain look/texture/etc just ask and I'll see if I can come up with a solution!