- create a new layer underneath the lineart layer (name it "colour" for organisation)
- colour the whole area over with the colours you want to use so there are absolutely no transparency gaps inside (you might have to go over the lines to ensure this); note: you don't want to leave any transparency gaps inside, otherwise your background colour will show through
- when you're done, pick the eraser tool (whilst still on your "colour" layer!) and erase the excess colour that has gone over the lines (without going inside the lines)
- method 1: pick black (or another dark shade - even dark purple works in some ways) from your colour picker and lower the opacity to something like 50% (you can lower it more to make the shading appear lighter)
- method 2: simply pick darker shades of the colour you're shading (this is the common method but it can be slightly annoying when you have to hunt for the exact right shade of a colour to make it work)
- Remember to name your layers and organise them into groups as soon as you start drawing (this can help a ton with organisation, hiding/showing layers and removing layers)
- Remember to mirror your image horizontally every so often (this will reveal a lot of your mistakes which you can correct as you go along rather than discover them all much too late)
- Remember to ALWAYS save! I've lost work in the past from not saving and it's the most annoying feeling you could ever imagine. To save yourself from this catastrophe, save your file before you even draw anything. After that, continually use the CTRL + S command at least every 5 minutes, or after doing something big.
- It's also just as important that you back your files up. As soon as I've finished drawing for the day, I back-up my drawing onto a memory stick and at a later day I email the drawings to myself as well (so I have a copy over the net) - although it would be best to use a medium like Google Drive. It's best to back up the original file (e.g. in my case, .kra) rather than the converted file (e.g in my case, .png) because assuming you lose the original file, the converted file will only have all the layers merged together into one.
Thanks for reading! If you have any questions concerning art advice or this drawing process at all please do ask them in the comments below! Also, if you're looking for a professional, free art program out there that is compatible with drawing tablets (e.g. Wacom), I highly recommend downloading Krita. It's easy to use, has a great range of tools and you can create so many things with it. (And no this isn't sponsored. xD)
Edit: I know I haven't named my layers here but don't be like me!