Just recently, I think it was yesterday, Donna showed how she put her fingers on the pieces as they were supposed to go through the needle and held them there as the piece went up to the needle.
A few months ago I saw someone else do what I always do. I hold onto the seam after I have it aligned the way I want it, a few inches from the needle. As it is going into the needle, with the other hand, hold the seam as it comes out from behind the needle. I actually pull on this seam as I let it go through as fast as the feed dogs want it to.
You wouldn't want to do this with bias seams, but bias seams are easier to line up anyway. Just keep the beginning and end in the right place and keep it flat as it goes through the needle.