Think in terms of difficult behaviors, not difficult people. When you catch yourself labeling people as difficult, focus on the present, identify the specific things they are doing that are difficult, and go from there. Some people will respond positively to the things that give them a sense of control. You might try giving difficult people more responsibility, or soliciting their input more often to see whether that has a positive effect. The garden-variety difficult person is someone whose behavior you consider difficult, but not in ways that are intentionally harmful, although the results may be quite destructive.
Managers often expect instant results when dealing with difficult people.
No technique is going to create instant results. Mediation is a process where a third party, the mediator, tries to facilitate a process where the disputing parties can solve their problems in a nonadversarial, noncoercive way. The venomous difficult person behaves in inappropriate or destructive ways in an intentional way. There is intent to damage others, which is absent with the garden-variety difficult employees. Progressive discipline is a process wherein an employee is notified of inappropriate behavior and where the sanctions and warning become firmer and more severe.