Use starsurge generally whenever possible, it's a nice spell.
Keep up moonfire on max amount of opponents, it ticks for sick damage even if you dont think so, keeps healers healing multiple people when you spam it around and keeps rogues from restealthing.
Use roots a lot, it's a great CC to have.
Memorize which races have which resistance racials so you dont gimp yourself wrathspamming a nelf or starfiring a gnome.
Don't forget to use rejuv + regrowth, they're both great spells even if you're not specced to healing.
Maybe post an armory link or some shit or explain where you need help in your PvP skills? I'm probably missing a lot in my post but these are just a few basics you'll definitely need to know playing balance. Also I don't know f2p stuff since I play 19s, so if anyone knows better, feel free to criticize.