Drawing is easy. You just need to know how.
Here is an example on how you can copy a complex drawing easily. Look at the object and ask yourself what shapes do you see inside it. How big is this shape compared to the other one.
3-dimensional drawings, especially flat ones, are also easy to draw. You'll first need a 2D drawing to copy from. Use the grid method to mark out your reference points. Draw an isometric surface and transfer those references point for point. If you draw 1:1 scale you simply measure the distances and mark your references. Finally draw isometric projection lines of equal length from the edges and join the lines up.
