How to 'clean' contacts?

Which lists should I keep up-to-date and what are the important aspects in 'cleaning' contacts

To be able to keep your database healthy, these are the lists to keep 'clean' (These are lists for Belgium but you can clone this and use it in other countries too)

2 important things here:

• Have the 'last checked’ on the actual date
• If the person changed to another company or no longer works there, make sure to change this association on the right side & put the right company as the ‘primary’ one, you can also add the association label of ‘previous employer’ to the previous