The beauty of variable frequency drive (VFD) is that the maintenance is negligible if are well maintained.
Tighten all nuts and bolts, all terminal blocks, cable/wire connections.
Remove dust everywhere (vacuum cleaner is good). Do not try any kind of solvent.
Check all power supply for correct voltage level.
Replace / clean filters.
GoHz maintenance plan do specify which component to change and when (for example blowers every 10 or 12 years).
If you have been trained to do so, check DC bus with oscilloscope (once is charged) to verify the Vdc ripple. Do not megger the VFD.
Monthly maintenance: Clean filters.
Weekly maintenance: pay attention to unusual noise from the converter (blowers or other components). Record ambient temperature, humidity, input voltage, dc bus voltage, output voltage, current and frequency. Record any temperature that the VFD is monitoring. This data will allow you and/or the manufacturer to provide guidance on planned maintenance or improvements to be implemented to extend lifetime.
VFD last 20-30 years if are properly ventilated, possibly installed in air conditioned room (25 degree is the usual temperature) with no presence of humidity / chemical agents. Furthermore do not switch them on/off daily but leave them energized and use start /stop if the configuration allows it.
If VFD is under maintenance, leave the heaters on (keep away humidity as far as possible).
If you leave filters dirty and dust accumulating inside the VFD the lifetime will considerably decrease. If input voltage is usually too hi, this reduces the margins on the Dc bus due to the capacitors. Change the tap of the input transformer (dedicated transformer or distribution transformer). Obviously this is done once forever.