You can't draw something without observing and studying what the thing you want to draw looks like. It's not possible to draw everything, so use references to help you out. Gather a few references from different angles of the object to understand it
Everything can be simplified into basic shapes, so apply this when you are sketching. Pick out basic shapes your object is made up of.
Drawing takes practice to master, so try drawing whenever you can to improve. If your art isn't improving try changing up the way you draw; experiment!