At this point until you are higher the motes of light are worthless. You can sometimes use them at Xur, the Weekend Special Vendor, to buy a yellow engram for potential exotic item but I havent seen that for a bit.
At 20, Do Crucible so you max out your 100 marks for the week. Do the same with vanguard playlists. You will be able to purchase purple armor using both from the class vendors and that will level you up. Do t he Daily Heroic Quests everyday at the highest level you can accomplish. Once you get a few levels into the 20s you can start trying to get through the Weekly Heroic Strike. Do as many bounties daily as you can. At this point there are several ways to get new weapons and armor.
1) Buy from Crucible or Vanguard Vendors using the marks from completing strikes and crucible matches
2) Leveling up your reputation levels with Crucible, Vanguard, Eris, Cryptarch will net you a chance at a purple item.
3) Random luck on drops and finishing crucible and vanguard events.
4) buying yellow items from Xur using the strange coins you earn from random events and Weekly Strikes.
5) Finishing Bounties randomly will give you an exotic bounty to earn an exotic weapon
Until you are 26/27 I wouldnt even try the Vault of Glass Raid and Crotas is out of the question until 31 IMHO. You are in a grind now, basically just do as much as possible with the goal of accumulating assets and items to gear up. Once you are high enough you can add Nightfall Strikes as well with a full group to earn some nice stuff.
Thats my simplistic newb advice from just having done this. Im not hardcore enough to get into multiple characters to max income and rewards.
A few additions...
Dont forget about the daily bounties. If youre a PvP guy, do the PvP ones, if youre a PvE guy do the PvE stuff. (PvE stuff is way easier and less grind) They give you faction standing with the appropriate vendor, vanguard for PvE and Crucible for PvP. Once youre vanguard rank 2 you can start buying the gear, boots and gloves to start with. Then for the chest you will need a vanguard commendation, this you get from turning the rep wheel for every rank after two. So at vanguard rank 3, 4, 5...etc... you will get commendations every time you ding the vanguard rank. Plus some other junk, even maybe a purple vanguard gun of some sort.
Marks (vanguard to buy the purple gear) can also be gained from doing planetary public events. There is a website something like destinypublicevents.com or some shit that has all the timers and where they pop. You can easily hit 100 marks in a day of grinding those, and all you have to do is show up shoot a couple of bullets and let the others around you complete them and you get full rewards. You also get the stuff you need (shards, energies) to level your gear and guns from them although its random....
Concentrate on getting the boots, gloves and chest and leveling those up as much as you can. Definitely do the strikes, the rewards are great, the blue engrams and a chance at purple engrams, even exotics for rewards although very rare.
Then at lv 27/28 or so you will want to go to destinylfg.net and spam for a VoG normal run. Watch a few videos before hand, but its not rocket science and this will be a great source for more shards and energies to level up your guns and gear. Even if you dont complete it, just doing a few phases of it and getting a few chests open is guaranteed shards and energies, plus a chance at some raid guns, exotic guns...etc...
The weekly dungeons should be done at the highest level you can do them at. I think now they are 24/26/30 and each of them awards 3 coins, or if you do the 26 you will get 6 coins and if you do the 30 first you will get all 9 so make friends.
I would not recommend buying a helmet from the vanguard guy. Its just too expensive. Save your strange coins and motes of light and wait for xur to sell an exotic helm or helm engram for motes of light that you can roll one for your class hopefully 33% chance. It does not really matter what it is just that its for your class and it gets you to a higher light level. Its all about light levels, the higher light level you are the more of the top end shit you can do that gives you the best rewards.
This will definitely get you to lv 30-31. Then you can start doing the nightfalls and crota raid at 31, you can even do the nightfall at lv 28 or 29 if you have a buddy or two to run you through them. MAKE FRIENDS!
