When you are in supercruise, do not look at your distance or your speed; look at your time to destination.
At or before you reach 20-15 seconds time-to-target or so, reduce your speed to the blue zone. Your time-to-target will hit 7 or 6 and stay there as your speed adjusts with the closing on the destination.
Using this method you will not ever overshoot.
Then you just have to wait to close within 1Mm and for yoru speed to drop below 1Mm/s and you will be able to use 'safe disengage'.
Once you get the hang of it it becomes second nature.
Also, I will sometimes just intentionally make a close pass to a planet near the target and use its gravity shadow to forcibly slow me to a near-stop, so that I do not overshoot by more than a few lightseconds, and then the trip to close on the target is a lot easier. This is best at the end of a long trip somewhere relatively far, and it is pleasingly similar to me to the method that the hyperdrive uses to pull you out of witchspace by using the star's gravity shadow.