Well, the trick that is really usefull is that the second colour is basically the negative space. So what I do is hard to put in words but easy to do in practice.

I use basic shapes like circles and curved lines to make hte frame in red and then I draw with the track pad (I’m on a laptop right now) in black. Then I select the main colour to be red and secondary colour to be white and erase with right click.

This makes the red frame be the only thing erased and leaves the black lines where they are. Then I use the bucket tool to get a majority of the spots correct.

To get the small spaces, I use the eraser trick in reverse. I make white the main colour and I make the secondary colour be the proper colour and erase.

Shading is done in the same way where the secondary colour is just a darker version of the main colour.

In essence, the eraser tool is my best friend.