How to level up past level 25?

Most gear, even when maxed out will not be able to get you to max level of 32. The only gear that will get you to level 32 is the gear you get from do the Crota Raid. Then if you max level them all and have 1 fully leveled exotic piece of gear you will hit level 32. It's much easier to get to level 31 though.

To get to 31 you only need 1 fully leveled exotic and the rest of your gear can be bought from the Vanguard or Crucible quartermaster. I recommend using an exotic Helm for your warlock because helms are more expensive to buy from the quartermaster than the other 3 pieces of gear.

The way I leveled my Warlock: Got an exotic helm and leveled it up. Bought Gauntlets, Boots, and Chest from Vanguard Quartermaster in the tower. Leveled those up. Now I am level 31.

A good way to get vanguard marks every day is to find Daily Public Events. You will get 4 marks every time you complete one and you can find them by using the website: DestinyPublicEvents.com. You can do them more than once per day. I know you can do it at least 3 times a day to get vanguard marks but you may be able to do them more than that. I can't remember if they stop after 3 times.

To get to Level 32: Play Crota raid as much as you can to get the raid gear now that you are level 31.

One last thing: The level cap will be raised from 32 to 34 with all new gear coming out in the newest expansion. The release date for the House of Wolves expansion is May 19th. The good news is that they will have a way to upgrade ANY legendary or exotic gear to be able to get you to level 34 when maxed out. So rest assured that the gear you are working towards now to get to level 31 or 32 will still be useful with the next expansion. Unlike how the last expansion made all our old gear practically worthless!

You might have all the legendary armor with 33 light, which would make you a lvl 31. The problem I see here is that you aren't upgrading them. They get more light as you upgrade them. Of you fully upgrade (incl. upgrade defense). And vanguard ranks are fast with bounties and patrol. Considering you do 5 bounties, it gives you ~350 reputation. The. it takes only 10 patrols to get 100 reputation (Note that Assasination patrols give you 25). If you have completed the Weekly nightfall strike, reputation gains are faster. You get about a quarter more rep. You get 31 instead of 25, 12 instead of 10, 125 instead of 100...

List of armor light (all fully leveled)

Crota's end gear and exotic armor = 36 light (full set level 32)

Vanguard, crucible and other common legendary armor = 33 light (Full set = level 31)

Vault of glass gear = 30 light (Full set = Level 30)

here is a list of light levels and the wiki page of light.

Your best bet for leveling from that point is to purchase a set of armor from the Vanguard vendor (or to hopefully find some). In order to find a legendary piece of armor at level 25, your best bet is to do the hardest setting available for the weekly heroic once, and after that just run the strike list.

It would also be advisable to save up about 13 strange coins so you can purchase an exotic item from Xur. This, in combination with a legendary set of light 33 will get you to level 31 when fully leveled.

Leveling armor is best done by completing bounties. If you are not into crucible (which I honestly cannot get enough of) you can still do the PvE bounties. There are 9-ish (depends on Eris's available bounties) bounties you can do per day. Doing all 9 and then turning them all in will level your armor very quickly.

Once you reach level 27 a lot more doors will open up. Doing the nightfall gives you a buff until the next reset which will grant extra experience gained from bounties and rewards (this will help with leveling armor). At this point you can also do the raids (if you find a group willing to carry you). DestinyLFG.com is a good place to find nightfall and raid groups.

tldr;

• Buy vendor armor
• Complete as many bounties per day as you can
• Do the Heroic Strike on hardest possible setting once a week
• Grind the strike list

Please note that with the most recent update if you perhaps get an etheric light as a random drop you can also upgrade your gear... but this is easily the hardest method.