Draw from reference.
Simply put, take any image from Google you like, and redraw it on paper to the best of your ability.
Not necessarily tracing, but that is also a good place to start to learn general shapes or curves.
A simple no-detail pen or pencil sketch would be good enough.
Draw lightly, so you can easily erase mistakes.
Stay focused. Take your time on each line, using multiple strokes to form the line.
Keep practicing a basic 2D pencil sketch, no shading, no texture, no color. Do this for a while, then when you feel you're ready, try new techneques. Hatching/crosshatching methods are perfect for beginners, especially with black ink pen.