I found its best to cut all the lines 1st.
Then I clean all the marker off the shell, as it just confuses things when you get going and are looking for the cut lines.
Make sure you use a few thin coats to build up each colour, also make sure it's not transparent / see through, which can happen if you don't lay enough paint down.
I he the painted area up to a light, if I can't see my hand through the painted area it's ok and I know the paint is thick enough.
Apart from that, you can't go far wrong. As said, you may want to re score the odd cut line once paint is down. Good luck
