Hi, I was in the same boat about 1 month ago because I didn’t really understand things about the game. The key to leveling up after Lvl 20 is doing a lot of Vanguard bounties and strikes to earn Vanguard reputation & marks (a form of currency) and then buying Legendary armor from your Vanguard which will increase your Light Level. Rare armor (Blue colored) can only hold a maximum of 21 light per piece, but Legendary armor can hold 33 light per piece and an exotic piece of armor can hold up to 36 light (armor you get as loot from the Crota raid also goes to 36 light). Of course you could also be lucky and find Legendary engrams and have those turn into armor you can use, but it’s very random so I never counted on that. Once you’re Vanguard rank is Level 2 and you have 75 Vanguard marks then you can purchase Legendary arm or leg armor. You’ll have to be Vanguard rank 3 to earn a commendation and then have even more Vanguard marks to buy a Legendary helmet (120 marks) or chest armor (75 marks). It may sound confusing, but focus on doing bounties and strikes and you’ll get there. For a better understanding of Light Leveling check out this page: http://destiny.wikia.com/wiki/Light. Using the table on that page, and the info I gave above, you can easily calculate how much light you’ll need each of your armor pieces to be in order to get to the level you want. I would also suggest searching the http://destiny.wikia.com site for the type of exotic armor available to your character and deciding early on what you want to go for. The reason for this is you don’t want to really invest much time & effort into obtaining a Legendary piece of armor and upgrading it only to subsequently replace it with an exotic piece. Xur comes to the Tower once a week and always sells exotic armor for each class for usually 13 Strange Coins. Keep in mind though his stock is random. This is why I still have a Rare helmet as I’m waiting for him to hopefully bring the exotic helmet i want soon.