Ok, I've got the following parts...

a small, fully working, calibrated CNC table,
a 0.3mm 3d print head,
a roll of 1.75mm PLA filament,
a pid temperature controller,
a psu,
a drive unit for the print head motor,

I have downloaded a sample .slt file of a nut and run it through Slic3r, this generated g-gode that looks suitable for my Mach 3 setup.

So, if I fit my head to the table, wire up the Pid controller to the psu and hot end, calibrate the extruder feed, set the head to zero on the table and run the code, what am I missing?

i know there are a million variables to fine tune, but have I missed anything vital before it gets messy?

Does printing start at ground zero or should the head be raised an amount, if so how much?

i know about glass beds etc but for a first run, surely a sheet of card would work just to squirt plastic on?