Wow these things got complicated. First off, if you want top rate information, head to arenajunkies.com – must have! They have macros, weapon and stat suggestions, what skills to use, talent trees, et al. If you want reaiding advice, head to elitistjerks.com, but for PVP – arenajunkies can’t be beaten.
Having said that, I learned a lot. In my defense, I’ve only just started PVPing on my DK – I tend to avoid melee DPS ever since the AoC debacle with the barbarian I had. (As an aside, I don’t know if Racy ever looked hotter in game…) So, I did hunter DPS for ages before Arenas even existed, and I’ve done my share of mage and ‘lock PVP as well. But I digress! Again!
I realized with my DK that I had no macros, which are apparently a must. I also know that I wasn’t maximizing my DPS, since I hadn’t reforged any gear. Heck, when I switched over to my DK, I hadn’t even enough money to gem out all my equipment on my mage.
So, you don’t just get gear. You have to do the following:
Get the right skills on your talent tree.
Determine what stats are going to prove necessary for your class. For example, for PVP, my DK’s stats (to max out, go in the following order, with Frost as my primary focus in my talent tree): 5% Hit Rating 
195 Spell Penetration Resilience Strength Mastery Haste Critical Strike Expertise.
Reforge your gear based on the above stats. Fortunately, it doesn’t cost a ton.
Get class/stat appropriate gems, as you gain slotted equipment. This actually may cost a ton. 
Set up macros for your spells/attacks. See Arena Junkies for some great suggestions.
Download recommended add-ons. Again, See Arena Junkies for some good ones. Dominoes, Bartender4 are a few that are must haves, IMO.
Start learning some of the class specific tricks. This is key. There are tricks to use as you cast your spells/use abilities and then there are tricks you can learn vs. specific classes, like rogues or priests.
If you want to get ahead in the Arena, yes, having some great equipment and class knowledge can help. That’s essentially how I played my hunter for years. However, there are going to be those teams who take advantage of every last trick in the book and it behooves you to do the same, even just to be able to last more than ten seconds, sometimes.
Good luck!
