I actually have to completely disagree with Connor on this one
When you throw your breakaway, make sure the yoyo is tilting toward you ever so slightly. Be swift - You dont want to die on you. I am assuming you are using a Dark Magic, and this is the reason it should be tilted. While the Dark Magic does have a thumb grind lip, it is not very deep.
Now while it is tilting, you are going to pop it up. I feel it helps to bend my thumb ever so slightly when doing thumb grinds. Now this part is the key: Dont try to stick your thumb in the lip, let the yoyo fall onto your thumb.
You will realize how important this is after you can do it. If you try to jam your thumb in, this will push the yoyo away, and you will never start to grind. But if the yoyo pops up, and kind of falls in place with your thumb, it will be able to revolve.
Also, when popping and trying to grind, make sure that you dont try to make the yoyo fall from a great distance.
That was kinda confusing, but I hope it helped!