Depending on the material of your vertical blinds you can follow the instructions for Venetian Blinds or Roman Blinds.

If the louvres have a plastic-type covering or are aluminium they will be suitable to wash with a damp cloth so you can follow the instructions for Venetian Blinds.
If the louvres are a heavy fabric then it would be better to use the hoover method as with Roman and Roller Blinds.