I'm gonna share some of my tips / bits of advice for how to BG proficiently.
While you are a Warlock that can tank a good deal of damage, it's generally far better for you to try & stand towards the back of battles, out of range of melee, to allow you to consistently nuke people down. Also, always be aware of your surroundings & nearby enemies. Throughout battles, you need to regularly check if you can better position yourself to better adapt to how your enemies have moved.
If you & some of your teammates are trying to kill someone, but they keep getting heals, don't be a derp & keep spamming your nukes on the guy; Fear the healer. If you see one of your teammates getting opened up on by a Rogue, Fear them to help your teammate out. Constantly look out for people needing peels, a quick Fear or Shadowfury can change the momentum in your favor.
Defend & Call Out Incs:
This speaks for itself, if you cap a node, be prepared to defend it. If you're with 2-3 other people at your node & you see someone call out in BG chat that there are a few incoming to Farm when you're at LM, be sure to go help them out as they likely won't be attacking LM soon & you'll be able to spare a person or 2. If you see people coming towards your node, call out in BG chat so you can get some help as soon as possible, don't be a hero & cost your team a node.
Fight On Nodes:
Don't waste your time dismounting to kill someone out in the middle of a road, if you aren't attacked first of course. It's more important to go attack a node & potentially secure the game for your team. On the subject of that, call out if you notice there are only 1-2 people defending an enemy node, state that they are vulnerable to a quick assault of 3 or so of you guys.
You will get a lot more accomplished with 1-2 other people with you. I usually serve as a 'floater' of sorts, traveling between nodes with a few others to respond to incs that were called out. Also, this saves you from being killed by some Rogue in a CS -> KS while mounted, which means no Soul Link for you!
Tada! You are now considered top tier BG Hero material, congratulations.