I keep a roll of blue painter's tape handy. I wrap it around my hand a few times, sticky side out, and stick it in a convenient spot on my sewing machine cabinet. All my thread ends get touched to this thread catcher. When it gets full, I throw it out and make another circle of painter's tape to replace it.
I use a large carpenter's T (purchased from a big box hardware store) to square my quilts after they are one.