It really helps when the seams all lay to one side or the other. When the seams flip from block to block, the foot has a tendency to jump the ditch (so-to-speak).
It also helps to make sure that your sandwich is pretty taught. That helps control the sides with your hands.
I roll my quilt into a tube and guide it through the throat. Sometimes, it gets very heavy and is hard to control. Sometimes, the sheer weight of it pulls the sewing piece out of whack. Take rests.
Lastly, go slow.