Pushing your jogging stroller uphill probably gets more thought than running downhill, but there are a couple important things to consider to run as quickly - and safely - as possible downhill.
How steep is the hill vs how heavy is your stroller? The first hill we go down at the start of our regular route is so steep that I actually walk backwards down it with the jogging stroller.
Generally, however, downhill is a great opportunity to cut a little time and to practice faster turnover (i.e. how quickly you put one foot in front of the other). This is just one of the reasons why jogging strollers have a hand brake and a runaway strap.
Even if it makes your arm get sweaty - ALWAYS USE YOUR RUNAWAY STRAP!
To use your hand brake effectively, you need to lean INTO it. As you squeeze the lever with your left hand, consider using only the palm of your right hand to push rather than gripping the handle which could inadvertently apply a downward force. This keeps the front wheel in contact with the ground (the only way the brake will work) plus it will put less pressure on your knees and keep your form better. You will maintain much more control than either trying to pull the stroller back or simply trying to run as fast as the stroller rolls.