Many people who think they are being assertive can come across as rude. They appear to be attempting to bully and shout people down and refuse to listen to the other person’s point of view. Unfortunately, they often mistake the hectoring style of Jeremy Paxman and his ilk as an example of assertive behaviour.
What assertiveness actually means is having the confidence to put your view across in a polite but determined way. It is all about not being used as a doormat.

There are a number of key areas which can be looked at, as this is potentially a complex area.
Staff need to examine their own feelings and how they can deal with them.

People need to recognise what their acceptable boundaries are and how to ensure that other people recognise those boundaries.

There are many coping mechanisms which can be practiced. For example, showing people how to bring unhelpful conversations to an end.

Staff have to learn how to say no and how to mean it without causing offence.
Anything that can be done to increase confidence is helpful.

People need to look at what are awkward situations for them and when they are most likely to occur. They should understand how to avoid those situations, or failing that, how to bring an end to those situations.
This can form a training course in its own right or be part of general soft skills training.