Things you should be working towards as a new 50

1. Hit and Focus.
You should be able to get enough from crafted pieces and reputation vendors.
T1 - 50
T2 - 100
T1 Raids - 200

2. Sigil of the Five.
You want one of these for each of your roles. They cost 7,500 Planarite and are sold by Quartmaster Melke in Sanctum.
It allows for 2 Greater and 4 Lesser Essences. If you are a Rogue DPS/Support you will want to use Lesser Essences in all of the slots.

3. Roles
You will want as many roles as you can afford. Trust me I can get into groups really fast because I can tank, support, and dps. Plus I
have two PvP roles

4. Planar Essences
The one's you want drop from Expert Rifts and Raid Rifts. You can also get many good one's from the Planar Rep Vendors in Sanctum itself using the currency you get from Expert Rifts, Raid Rifts, and Zone Invasions.

5. PvP
Once you hit Level 50 you can start gaining Prestige. This allows you to go up in Rank, which in turn allows you to get better PvP gear. The PvP gear will help you stay alive longer. Some of it is even pretty good for PvE, but make sure you're meeting #1.

6. Having Fun
Don't grind endlessly and burn yourself out. The game has a ton to do, so do it how, when, and what you want.

I would like to add to this that priority in gear should be get all crafted gear you can for your toon, depending on your main role (at first then you spread gear over other roles) and pvp gear. I would skip T1 gear all together and save up my plaques for T2 gear unless you're a tank. Otherwise you can get away with what I'm saying. From there it's really about doing the random T2 dailies and doing raid rifts to get BiS pre raid.