Determine the limits and overall structural "scaffold".

Block in the rough shapes of the elements of the design (I prefer using black ball-pen).

Now convert those rough shapes into more realistic sketches, keeping the main line thrusts in tune with your "scaffolding".

Now, using pencil, redraw the elements as you wish them to appear in the final work. Still maintain the control of the lines of the "scaffolding".

Use side sketches to determine the fine details and drawing decisions --- especially for the arms and the mantling.  Trace the eventual drawings back into the final work.

Finally, ink in or colour it. §