Vanguards / Powertechs are the only advanced class that can pull enemies to them. [Edit: As well as Assassins / Shadows, although they need to spec fairly deep into their tank tree to get their pull, while VGs & PTs get theirs at lv. 22] This makes them particularly dangerous in Huttball, where one quick yank onto a Fire Panel usually translates to death. If you see a Powertech or Vanguard near a panel or near the acid pit, try to keep a barricade between you so that, even if they Grapple / Harpoon you, the barricade will stop your momentum.
When ambushing Sages / Sorcerers or Commandos / Mercenaries in melee range, use any anti-knockback buffs within the first five seconds of the fight. These classes have access to AoE knockback abilities, and they tend to panic whenever an enemy is on them, so their first instinct is to immediately use their knockback skill. Once that fails, their second instinct is to stun you, so if you really want to get them, be ready to use your CC-breaker ability.
Powerups are essential to maximizing your Warzone potential. In every Warzone there are three potential powerups: Damage / Healing (+% Damage and +% Healing), Speed (+Movement Speed) and Health (Instant Heal). Knowing where these powerups are can let you swing 1v1 fights by running to them for a quick heal.
Warzone Commendations cap at 1,000. If you get near the cap, either convert those Warzone Commendations into Mercenary Commendations (3:1 ratio) or purchase some items with those commendations.
Regular medpacks and PvP-only medpacks are currently on separate cooldowns, so if you really think you can score that Huttball with an extra 3,000 heal, pop both for a mega heal.
Healing is currently very strong in PvP, especially with tanks being able to mitigate a lot of team damage. If you can heal and you want to win more Warzones, learn to heal.
Line-of-sight is very well done in SWTOR, which means you should try not to fight in open spaces, as this opens you up to all sorts of sniper fire. Instead, fight near pillars or under ledges so that you can evade shots when possible.
Even if there are no hazards nearby, be sure to push or separate tanks from their healers. Tanks can Guard their healers, which significantly reduces the damage the healer takes. Pushing them apart outranges the Guard ability, thereby allowing you to freely DPS the healer.