The Rapala Knot makes a small fixed loop that allows a fishing luer to move realistically. It is recommended for plugs, but it will suit any sort of lure of fly that needs freedom to wriggle or wobble about enticingly.
To Tie a Rapala Knot:
Tie an overhand knot. Leave 5" of free end. Run free end through the eyelet.
Run free end back through overhand knot.
Wrap free end around standing part of line 3 times.