Node.js: How to run asynchronous code sequentially

I have this chunk of code

     User.find({}, function(err, users)
      {
        for (var i = 0; i < users.length; i++)
        {
        pseudocode
          Friend.find({'user':curUser._id}, function(err, friends) **ANOTHER CALLBACK**
          {
            for (var i = 0; i < friends.length; i++)
            {
  pseudocode
            }
            console.log("HERE I'm CHECKING " + curUser);
            if (curUser.websiteaccount != "None")
            {
              request.post({url:'blah', formData: blah}, function(err, httpResponse, body){ **ANOTHER CALLBACK**
pseudocode
              sendMail(friendResults, curUser);
            });
            }
            else 
            {
pseudocode
            sendMail(friendResults, curUser);
            }
          });
    console.log("finished friend");
    console.log(friendResults);
    sleep.sleep(15);
    console.log("finished waiting");
    console.log(friendResults);
        }
      });

There's a couple asynchronous things happening here. For each user, I want to find their relevant friends and concat them to a variable. I then want to check if that user has a website account, and if so, make a post request and grab some information there. Only thing is, that everything is happening out of order since the code isn't waiting for the callbacks to finish. I've been using a sleep but that doesn't solve the problem either since it's still jumbled.

I've looked into async, but these functions are intertwined and not really separate, so I wasn't sure how it'd work with async either.

Any suggestions to get this code to run sequentially?

Thanks!