What knots and whatnots

Most knots in suturing are variations on the reef knot.

You will see many authors advocating multiple throws, even 6 or more on nylon sutures. This might apply to tough thick sutures, greater than 3/0 calibre, but for the typical thread you use for skin, three throws properly applied are plenty to hold things. 

Try to get the tension about right with the first throw just enough to bring skin edges together. But with a reef knot, you can cinch up or tighten that first throw by applying a bit on tension on the second throw.

Once the third throw is on, you cannot move the knot. Use more throws after this and you are just wasting time and thread.

See link to Surgeon's knot below for a good example of the basic steps.