I'm a newbie to digital colouring. I haven't worked digitally before but not with layer modes, masks and textures and I learned a lot and am very satisfied with the result, thanks to you, Sara!!! Oh, and I used GIMP. Here's my process:

I chose a globe as my drawing object and made these 2 min sketches:

Went for no. 4 and made my handrawn linework without any shadowing:

Scanned it and did clean-up and tracing paths for colouring and then I just played around according to all your tips - layer modes and masks and textures which I hadn't done before. I used the following textures:

 

 

 

 

 

and this picture of a glass sphere for the reflections:

End result is this:

Thanks again, Sara for teaching me!