Lubricate the line with saliva before cinching up your knots. Otherwise the cinching process will create a surprising amount of heat which will damage the monofilament and weaken the knot. This is especially uncool when tying on tippet sections, where knot breaking strength is important.
Many anglers tie a given knot correctly only to lose it when cinching the knot tight.
Lubricate your knots and carefully cinch them tight. Try to keep the knots neat. This is the number one mistake we see.