How do you communicate with a devil?

First you might find one... I don't think they really exist; rather, I see the Devil or devils as a symbolism for everything that is evil.

However, if we assume for the sake of argument that devils exist, I would recommend to stay away from them. According to all the stories, they are rather evil, and traitorous - in summary, contacting them would be dangerous.

Another answer:

Contacting evil spirits is not advised, but to answer the question, you would form the intent to speak to a devil and speak or think what you want to say. When speaking to spirits, you generally should not speak to them, and particularly not ask them to help you with something, unless you know their name. Assuming the spirit world exists, there is no reason to think it operates much differently than the current world. For instance, you would not leave your front door open and holler out for anyone who wants to enter to do so. Harm would likely result. So likewise, you would not want to summon random spirits and invite them to converse with you.