Practice,practice, practice and then practice some more. Tactics are what separates the good from the not so good, but gear also plays an important role. Make sure that all of your gear items grant you a power and not just a boost in stats. You have to be well rounded regardless of your class and this means you will need to un-equip some of the flashier damage dealing gear for other items that provide you with shielding and/or healing while also giving your stats a boost. This kind of gear is available for all classes, but sometimes requires several hours of 'farming' to acquire. For example...on my Swashbuckler I resisted the urge to equip an item that would have given me another Assassin's Strike and another Walk In Shadows in favor of some boots that give me Valor's Fortress along with a weapons and dodge boost. Not as flashy, but much more practical. I have a gear item that gives Revive along with a dodge boost also. After you pvp a few times you will see that you only need so many attacks. Shielding and healing can make all the difference. Go to the brawling hall and 'click' on some of the good players of your class. View the items they carry and then try to obtain them for yourself. After you have pvp'ed a few times you will see that there is a basic strategy for each class and with just a few tweaks you can adapt it to serve you against any class or circumstance. Know your classes strengths and weakness and after you lose a match ask yourself...'why did I lose and how could I have avoided it?" You'll get there if that's what you want. All you need is...practice.
What class are You? Each class usually has a generic cannon strategy, mixed in with their own, to produce great pvpers. As Spiral Cowboy said, gear makes the difference too. Also have good companions, though your character does most the work you need good supporters too, bodyguards basically. And remember, if you lose the first time, blame it on your parents-no, try try again.