I was contacted about good calibration prints for the Monoprice Select Mini, and beyond the usual (Benchy, etc) I said that all I use is a first layer test, as most of the time that's most of the battle. Couldn't attach the file to a Thingiverse direct message, so figured I might as well post it if anyone else was interested.
How I created it
This is just a 100x100x0.25mm block sliced in Cura with no top or bottom layers and a 20% infill. This results in two shells and one layer of infill which results in a quick print that gives you a good indication of the consistency of your bed levelling.
I was also going to advertise this as "DIY fishnet" but I think I'll leave that to Sexy Cyborg