Most of the changes I made, I either got from, or published on, Thingiverse.com, a site devoted primarily to 3D printing and takes it's format directly from Instructables.
The links I provide will take you directly to the "thing" I've added to my printer. Hit your return button to get back.
One of the first additions I made was to permanently mount a precision height gauge
that measures the distance between the extruder heads and the build surface.
I'm not a big fan of digital tools. The gauge I use is mechanical, and looks quite at home sitting on top of the Jules Verne printer's extruders.