You don't really need measurements in drawing.I drew my whole life and I honestly never scaled.

My method...
Learn and improve on yuorself.Honestly.

First,imagine what you want to draw and scan it into your head.
Then,draw a rough sketch.
Next,Add outlines and colors(if it's a color drawing) to make it take shape.
After that,remove the lines on the rough sketch to make a claer picture.
Finally,add some stylish text.

Honest of all the above.Keep your efforts up,though.