Two ingredients are needed, and only two:
To believe thoughts we send out get where they should go, requires acknowledgement. We're conditioned to expect it at a specific pace; sending a letter in the mail, talking, e-mail or text messages all carry very different expectations.
Humans also learn specific acknowledgement. To send a letter to the telephone company, dropping the envelope with a stamp in a mailbox, creates ZERO expectation the answer will come by text message.
Humans acknowledge incoming replies by reading or hearing them but NOT by thought. This is curious because all physical movement, including writing and of course speech, first require THOUGHT. That is easy to understand but most people curiously exclude from it the idea that thoughts are the basis of spoken and written communication. Humans generally believe thoughts are captive to the insides of our heads.
The best way to create belief is to see it happen in a way that fits already established, accepted ideas a person holds. Most of us are unaware of what we believe until we trip over or are struck by something which doesn't fit, something that makes no sense. To see a burning candle's flame point straight down, heat dropping not rising, crashes head-on into beliefs everybody has about burning candles.
Do you believe your thoughts directed to a person or to a soul arrive as intended? Once you do, recognizing the reply becomes easier and easier.
Ever hear somebody mumble or stumble words? This is human speech function unable to keep up. Throwing tennis balls, one at a time into open cardboard boxes passing by on a conveyor belt, is much easier with slow & few than many going fast.
The speed a human mouth, tongue and voice box can put out words is limited to much slower than brain speed, which itself is slower than mind speed. Our minds beat every supercomputer with a stick.
Written or spoken communication going out, are thought turned into speech or writing. Telepathic thought arrives faster and clearer. None of the mess words, characters, speech or writing make, gets in the way.
The challenge is: separating our own thoughts from what enters.
Rinse and repeat, rinse and repeat, rinse and repeat. Like a diet, it does not work immediately. It's necessary to continue, as often as one wants to try. At a specific point, things will "click on" and almost suddenly will come the ability to separate own thoughts from incoming.