Double Uni Knot
Easy to tie and very dependable. As the name implies, you tie two Uni Knots and draw them together. The double uni knot will cope with lines of differing diameters, and will also handle both braided and monofilament lines. Use a minimum of three turns with monofilament, but double this for braided lines.
Always remember to lubricate the knot with saliva or water before tightening.