VERY good advice. While I've been dealing with all my stuff these last few months, I've had a lot of people saying 'just let me know how I can help'. Well, bringing dinner over, mowing the lawn, doing dishes, that all needed to be done and I had no energy to do it myself but I never asked anyone to do it. People wanted to take me out to eat, I didn't want to socialize, I would have much preferred a casserole or something dropped off. I would mention to a few people that my house needed to be cleaned or my dishes needed to be done, but I didn't outright ask and no one picked up on my hinting at it.
So, don't just offer to help, offer something specific. Don't wait to be asked, just think of something that would help you if tables were turned, and dio it for your friend.