There are quite a variety of mechanical advantage systems to choose from providing different levels of pulling advantage.  The common ones are:

It's a very good safety practice to estimate the load at the anchor point and the object you are pulling to ensure your rope strength exceeds that load.  Another good practicce is placing a weight (damper) a few feet from the object you are pulling.  If the grab loop handle snaps, the damper will provide a drag for the rope and carabiner to prevent it from flying back at the pullers.  Speaking of the pullers, they should be wearing theor PFDs and helmets.  Finally, a racheting system can be quite handy.  This is easily constructed by attaching a Prusik line to the main line and attaching the other end to the anchor.  If you need to let go, this brake line will stop the line from completely paying out and acts as a line capture device.