The best way to dry down is in a tumble dryer. Always check the care label of your jacket for guidance on heat settings.
Every 20-30 minutes, check your jacket by removing it from the dryer, shaking it out and pulling the clusters apart. Ensure it is totally dry to avoid any clumps, then air it out for a few days.
An easy mistake to make is tumble drying your down jacket until the outer fabric is dry, assuming that the down clusters inside are also dry. When down gets wet, the clusters collapse and form clumps, and if left to dry like this the jacket will be rendered useless and will need to be replaced.
Store your jacket uncompressed and do your very best to keep it dry - always bring a waterproof shell with you to protect your jacket in the event of rain.