Start by cleaning things up.
Then check all the mechanical aspects — the basic points of adjustment for a machine are:
-
(for belt drive machines) Pulley set screws — verify that these are in-place and secure — be sure to check all axes/pulleys (including Z on machines w/ belt-drive Z-axis, for an HDZ, check both coupler screws).
-
(for the SO3/4, X- and Y-axes, and the belt-drive Z-axis on Launch and summer 2016 SO3s) V wheels / eccentric nuts (per assembly instructions)
-
(for belt drive machines) Belt tension (see the relevant step in your instruction manual, Note that the X-axis motor is held in place on standoffs and if those bolts are loose this can cause belt tension issues. Also, belt tension for the Y-axis stepper motors needs to be even/equivalent on each side — a significant difference can cause skipping on one side eventually resulting in lost steps on both. Measuring belt tension, squaring and calibration
Naturally, this assumes that all the wiring is in good condition and all connectors secure per the Machine Operating Checklist.