If you need a specific need met, be specific, says Bonior. For example, if they text you constantly, an easy boundary to set is letting them know that you can't text them back during the workday because it's affecting your performance (or, you know, your boss is starting to get pissed).
But if you're just looking to take a step back from the friendship in general, then you might not be able to give them exact guidelines and that's OK. In that case, Bonior recommends saying something like, "I still want to be able to hang out, but I have to admit I just can't do it as much as I used to because my life is changing."
And if your friend doesn't respect those boundaries, then you might need to reevaluate things again and try one of the other routes.