Starting in the middle and alternating directions will help your quilt lay flatter and you shouldn't get puckers either.
I like to use a wobble stitch. It is a very narrow zig zag stitch. It reinforces the seams, as the needle takes a bite on both sides of the seam.
It is very forgiving, if you miss here and there, too :wink:
Varigated thread is wonderful on scrappy quilts :D:D:D