My son wanted to create the animal rescue center from Go Diego Go so I offered to make a hammock for Diego to sleep in. This guide shows a 9-strand hammock, but I think using 12 strands would make it a better width.
Step 1: Cut and tape the strings
I used 9 strings about the length of my arm - the size depends on the size of your doll. Unless you have a very patient and helpful young person to hold the strings, I suggest knotting the ends and taping them to your table. My son was anxious for the results, but not so helpful in holding things still.
Step 2: Braid the end
I like the braids to go from one fat braid to two thinner braids to three thinnest braids. If you're doing 12 strands, you could even do four 3-string braids. This helps the hammock have a more oval shape, rather than going from the knot to the width of the hammock.
Step 3: Start the knots
Starting from the left (or the right, if you prefer, I just find it easier to keep going in the same direction, left to right, left to right, rather than going back and forth) take the first two strings and knot them. Take the next two strings and knot them. Continue til there are either zero or one strings left. For the next row, leave one string untied on the left, then take the second string (from the first knot) and the third string (from the second knot) and knot them together.