If you are a new player to Brink, there's a few things you need to know about the game, If you're a returning Vet, there's a good chance you've already heard all this before. I've put together a list of a few things on how to get the most out of such a great game without having to buy the DLC even though most players will encourage it.
Brink isn't like most other FPS's. It isn't a silly arcade Shooter where you run around all lone wolf-like trying to "rack kills to win". It's an Objective-based game where you and your team must WORK TOGETHER to achieve victory. There are no kill-streak rewards, so don't expect to drop nuclear warheads if you're doing good. If you're doing good, it'll show in the enemy team, and you'll be pushing the lines in your favor.
Now that introductions are out of the way, when you first make a Character, make sure to do the challenges immediatly, as it will unlock attachments and weapons. Also, it is easiest to do these at lower levels since the AI will upgrade with you. As you level up and try the different guns (there are a lot of them) you'll find you're favorite pretty easilly and put the attachments that you like the most on them. Please note, you can have more than one attachment on your weapon, and each of them has a distinctive effect on each weapon. You'll also unlock new outfits and Head gear, each of them are able to be customised to suit your taste.
Player body types are part of the customisation aspect as well. Each one has it's strengths and weaknesses that are up to you to decide on. Also note that while these body types have different aspects to them, they are also there to help you adapt to the game better, allowing you, the player, to decide the pace you want the action to be at. No other game to date allows you to set the pace of the action.
It's best to create a character that can perform multiple roles, since you can't change characters in the middle of a match. Even though there are players that have perks in all classes, I find that it is best to limit yourself to two classes, to maximize your effectivness on the field. Also, have a few characters that mix different classes, so you have options before you enter a match.
I think that covers most of it, so have fun out there on the Ark, and I look forward to seeing you there, no matter which side you fight for.