i have a zero center measuring tape that i'm able to use for most of my quilts.
the length is 120 inches and the zero is in the center and it measures out 60 inches in each direction.
i square my quilt first. then i use this measuring tape to mark along the quilt on all 4 sides at the same intervals. if its an open breezy type of pattern i might mark at every 6 or 8 inches depending on the length of the quilt.
if its a tight complex quilting pattern i might mark the quilt every 2 inches. this allows you to have the exact same motif land in the exact same spot on each side of the borders (if you happen to be an OCD kinda person).
i only go to this much trouble when there isn't a stencil available on the market that i can use.
i use plastic stencils and paper stencils. i like the software quilting designs by quiltmaker. they make 6 different programs (the 7th will be out soon).
http://www.electricquilt.com/Shop/Quilting/Quilting.asp
they cost about the price of 2 plastic stencils except with the software you can size the stencil to whatever size you like and then print it out on paper, attach to the quilt, and stitch.
here's a pic of one of the quilt maker stencils that i sized to fit my block. it has a center feature and then a scroll around it.
this is the master copy that i keep beside me while i quilt because i marked it with the start, the direction to travel in, and where to stop.
i just tape it to my quilt with painters tape and quilt right thru it. if i'm working on a quilt that i don't want to wash when i'm done i'll needle punch the paper and then pounce the design onto the quilt.