I will start off by saying that when you loose, most of the time its because you missed something in this post. Not because your class sucks or your enemies class is overpowered. Remember its PvP, you will die. If you are dying alot take a look at this post, and try to improve.
Remember: "Do or do not, there is no try!"
1. Know your enemy.
-Simple enough. Know your target understand how they play. What thier advantages and disadvantages are. The more you know about your enemy the easier it is to thwart him/her.
2. Pay attention to the fight, and watch your enemys moves.
-Spamming buttons usually gets you dead fast because your not really watching what your enemy is doing... your spamming damage and cc without thinking.
3. Perseverance.
-Hang in there because many fights are won with barely any life left. A sifu once told me that only a fool goes into a fight thinking they will not get hurt.
Things to be aware of in PvP:
1. Levels matter but less so as you level.
-People are complaining about not being able to kill so and so or whatever, but they have not even made it to thier early 20's. About early to mid 20's in this game you will have most of your skills... not all but most. What your class cant do in the teens they will be able to do later on.
2. Focus Fire! Focus Fire! Focus Fire! Your Enemy will and so should you!
-I dont know what gives, but every mmo I have ever played with in a pug, including warzones, no one focus fires. They all want to go off on thier own and save the world by killing the bad guy. Dont do this. Work as a team and focus fire!
3. Dont spam your abilities!
-Time your abilities. Its rediculous to think your gonna be able to win without thinking about what you do. Remember Patience.
4. Know your objectives.
-Know what it takes to win in your warzone. Work as a team and do those objectives.
5. Team work.
-Dont wander around alone. Work with your team, not against them. You fail your team when you fail yourself and get owned for not working together.
This is only a start. There are lots of things to remember when PvPing. I am sure others will help fill this in. Pay attention and you will win more and live longer!
** I forgot one thing. Remember you can use Stims, and Health pacs. Your enemy is going to so you might as well do it also. You can find them on the vendors, and there are even pvp packs you can buy right in the warzone at the beginning. Also the GTN will have the better stims and medpacs that the crafters can make.