This is the title of one of the more intelligent and practical Sales books I’ve read. My own method is complete directness, making it obvious I am trying to sell something, but only if it makes sense for the client. People who have problems that need solving always appreciate help, if it is competent and well intentioned.
When it comes to debate, it seems to me that broadly speaking–and there are infinite local variations possible–there are two types: efforts at persuasion, and efforts at learning. We get them confused.
In general, my interest is in learning. I am not always kind and gentle with people I debate, if I perceive them as being more or less consciously obstructionistic and obtuse. This is because I like pushing, and getting push-back. This has been a reliable method for me over the years of generating new insights, and new perspectives on old ideas. This is not, however, persuasion.
In persuading, the very first task is determining if the person you are talking with CAN be persuaded. Are they conscious of a gap or defect, or do they suspect one may be there? Are they trying to solve a problem, that they will appreciate competent and well intentioned help on? If not, there is no point in talking with that person.
If so, then the first thing you have to do is demonstrate empathy and understanding, such that they will listen to you. Where there is no connection, there is no useful communication, and there can be no connection where there is no openness.
This is a suggestion I am making publicly to myself, but I think it is always worth devoting a bit of time to determining what type of discussion is happening, and a bit more to what type of discussion is POSSIBLE, in any given context.