This can't be original but I've not made any before. Triggered by seeing some near infinitely expensive plastic moulding from Rutlands the other day and the need to clamp up my barrister bookcase prototype.
I made 4 in about 1/4hr. I think the pictures tell it all really.
A small chamfer on the 90 degree corner helps stop any glue squeeze out from attaching the jig to the work.
They are a pleasure to use and easily made from scrap.
Oh yes and take the time to set/check your TS cuts perfectly square. In the process I noticed everyone of my woodworking try-squares was in error on one face of other. I ended up machining it truly square on the milling machine and marking it "OK". The others will get the treatment on a round-2-it basis.
Bob