If the quilt is not too big I mark the lines across the quilt and start with the longest one in the middle of the quilt. I then do the next to one side and continue until that side is done. I then go back to the middle of the quilt and do that side from the middle out. You need to make sure the quilt is very flat, otherwise you will have puckering when you do the other direction. At this time it doesn't really matter where you start, because your quilt is already held in place, but is very important to use the walking foot. Even feed now will prevent your fabric from puckering against the lines already quilted. If it is a large quilt I avoid straight lines at any cost. To me FMQ is easier if the quilt is too big.
Maria