I tied off to a stake or weight on the ground. This has the advantage of being able to move the limb both vertically and horizontally. So you can often move it to fill in an opening in the canopy rather than just pulling it down.

I tie a short loop in the string about a foot short of the limb and run the string over the limb and tie off to the top. This way the limb isn't girdled.

I do both. I use a strap or at least several loops if it's string so like fruitnut said, it doesn't girdle the branch. Sometimes I use a section of bicycle inner tube so it's not too much pressure on one point.
John S
PDX OR

14 guage wire. it's the easiest thing around and reusable go to www.qdmaforums.com and search for wire and training lots of good info on how to do it

Garden string and a big rock.

I've done both. I've had issues messing up buds with wire, so I use wood spreaders and/or hanging stuff.

Commercial growers often use spreaders because they are quick and affective. Weights are difficult because what seems right might be too heavy over time and you end up with a broken or pendulant branch.

Here's a link where you can buy individual Treform spreaders which are quite excellent.

Here is a link that might be useful: treform spreaders

I use 7 inch rubber bands to pull down my limbs tied to the central leader or support pole. They are cheap and a quick install.

Here is a link that might be useful: 7 inch bands