I have 2 methods.

When I shot the 3D circuits I used to cut the distance in half and judge half the distance then double it. It is much easier to judge half the distance.

I also used the 10's. Divide it into 10yd increments.

On shots over 50yds I did both.

The best practice in the world for judging distance is to go for a walk and constantly judge things in your path then step it off as you go. The key here is to NOT change your steps or paces to match your yardage. Change your estimate. Your steps will always be your steps (unless you get a bum leg...LOL) and work on guessing how many of YOUR steps it takes to get there.

The best bit of advice I can give you on distance is that if you do not use a range finder then ALWAYS...and I mean ALWAYS use YOUR YARDAGE.
By that I mean whatever you step off as 10yds IS 10yds...Don't worry about what a yardstick says. Use YOUR yardage that YOU estimate and set your pins or adj sight marks accordingly. My yardage is just a tad longer than the yardstick...but that's fine. For me I use MY yardage. My 20yd shot would measure out around 22 actually. My 50 would measure about 54-55 yds on a rangefinder, but to me it's 50 and that is where I hold for.
See what I mean?