The Anchor Bend Knot (aka the Fisherman's Bend Knot) is a very strong knot that can be used to attach line to a number of items in a pinch. It is so reliable that it was was traditionally used by sailors to attach their line to their anchors. It works well for attaching fishing line to hooks, though we believe there are better knots for use with monofilament line these days.
Figure out what you're tying on to and make a complete turn around the eye/ loop of the item. Take the bitter end (the short end) and bring it around behind the standing end ultimately sending the bitter end back through the original loop.
Pull on the bitter end until tightened. This knot can be easily undone but does not slip, especially if you use a half hitch for added security as shown here.