The most straightforward method is to do a ton of strikes to build Vanguard rank. You will get some legendary stuff as drops/rewards, and when your Vanguard rank is high enough, you can buy whatever else you need. All legendary armor (helmet, chest, arm, leg) when fully upgraded gets you to level 30. You can also do this via Crucible if that's easier for you than PvE. By then, you may get an exotic piece of armor in a drop or if not, you can buy one from Xur. If you buy from Xur, be selective and consider the perks and stats heavily. All legendary + one exotic, when fully upgraded, gets you to level 31. To get to level 32, you'll need raid armor.