I've found the exact opposite, there's no way I'm going to get all my friends and family to install Telegram and set up an account just for me. That's why it's pretty unreasonable to casually propose Telegram as a replacement for solutions like Whatsapp. Unless it lets me talk to users on other platforms (how would it even do that?), Messenger and Whatsapp are here to stay.

Just start by installing it.

Chances are you'll see a number of your friends have it installed already as others have noted in this thread.

Then talk about it to your friends, show them the stuff you know they will love. For some it is bots. For others it is themes. Hashtags to follow topics. The possibility to have a chat with yourself (I run a journal like thingy where I note when I check oil on my car, when I changed my contacts etc, all hashtagged so I can retrieve it by tag later.)