Milestones are the best way of acquiring new, more powerful equipment. Moreover, you can also complete a Flashpoint task that appear each Tuesday and happens on a different planet. Flashpoints are special Milestones that offer better rewards and are more prominent. To begin a new Flashpoint you need to perform a certain amount of Patrols, return to Cayde-6 in the Tower and take part in certain amount of Public Events. If you've managed to reach the required amount, you'll receive a legendary engram which is better than the one received from NPCs and can yield an exotic item as a reward.
If you want to learn more about Flashpoints and their rewards, visit Bungie's page which receives constant updates on the current events:
The monthly articles contain a calendar with every planned event.