Now , I judge in increments as well ! I have a pretty good idea of where 20 yrds is in just about any terrain (open fields still get me a little).......and just double it for 40 and so on........and typically I'm within 2-4 yrds !
When I first got started I tried to do the same, tried guessing and stepping off, tried a rangefinder, etc. ........all helped ! But I got a tip on throwing arrows randomly around the yard.......and shooting from where ever they landed and starting out ....it helped me the most ! I stretched things out after I got that down !
One more tip........use real expensive arrows.......I used A/C/C's in the beginning ! After you lose several of them at $12 bucks a pop.......somehow ......the learning curve speeds up quite a bit !!
Good Luck !!