Can you recommend any methods for guaranteeing that...

Can you recommend any methods for guaranteeing that participants in a 360-degree feedback evaluation offer sincere and beneficial feedback? More specifically, how can I {specify a certain approach or tactic}, while also considering any {particular cultural or social aspects} that might influence the process of giving feedback? How can I ensure that participants feel at ease sharing both positive and negative feedback, and that the resulting feedback is well-rounded and perceptive?