Kevan Lee from Buffer has quite the article on copy.  Check it out, today.

“Join us!”
“Sign up!”
These phrases litter the huge variety of email newsletter boxes you’ll come across online, and they generally serve the same purpose: Click here to give us your email address. They serve the same purpose, but do they say the same thing?
Can one word change the way you feel about a button?
In my experience, yes. I subscribe to the copywriting school of thought where every single word is absolutely worth stewing over and A/B testing because one single word can change everything. The difference between “joining” and “signing up” is the difference between fellowship and enlisting. A word changes the meaning, the mood, and the motivation.  Keep reading.