How can I draw an apple the way I would do a pop art painting?

Try to not add too much detail to the shapes within the apple. Use bright colors, like red, yellow and green. Don't add outlines, it may be hard but it's actually very easy, just outline each part using the color that will be within it, such as a red outline, for the body of the apple with the same shade of red for the fill. It's also a good idea to use yellow for the shine effect that's on the apple. Have the opposite color of the apple as the background (use a color wheel) -- the opposite of that color makes colors more popping.