Johnny asked me the other night, and it's a little hard to answer that in a brief manner. Basic point breakdown:
+50 for enemy kill
+10 for kill assist, +30 for a critical kill assist (do most of the damage but don't finish the job)
+50 additional points for double kill.
+10 additional points for headshot (not sniper)
+50 additional points to your kill if you kill someone attacking a team mate (savior bonus)
+50 additional points for killing the guy that just killed a teammate (avenger bonus)
+100 for taking out objective
+80 points for capturing a flag
+50 points for a flag capture assist
+20 points for Spot Assist
+30 points for severe vehicle damage
+30 points for turret destruction
+100 points for vehicle destruction
+50 points for vehicle destroy assist
Main thing for boosting points, stick with your squad. Squad adds bonuses to all of your point earnings, in addition to some various squad bonus related pins.
+30 additional for enemy kill in order radius (objective kill/defensive kill) - make sure you're setting orders, default is 'q' while cursor is hovering over an objective
+10 additional points for squad kill assist (wound a guy and a squaddie finishes, so +20 or +40)
+30 additional points for squad order capture
Assault:
+10 points per tick with resupply
+10 additional points for resupply in radius
+10 additional points for resupply squad mate
- Note: Moderate to long range, moderate power assault rifles with added grenade launcher (or C4 if you use a shotgun), makes this class best for assaulting objectives and sustaining a decent K:D, and their score relies on that. Also the only infantry class to get smoke, key for breaking spotting.
Engineer:
+20 points per tick with repair or disrepair
+20 additional points per tick for squad vehicle repair
- Note: Light weapons, but has tank repair and anti-armor secondaries. Makes the engineer a high priority target, but can still get a lot of points while staying well behind the front lines. Makes for a decent stealth class too with the close range advantage.
Medic:
+10 points per tick for healing
+10 additional points for heals in objective radius
+10 additional points for squad heals
+50 points for revive
+10 additional points for revive in objective radius
+? additional points for squad revive
- Note: LMG's are more accurate from sustained fire. Dig in, drop your kits, and then light up everything you see. Medic is the healer and the squad automatic weapons guy. Heal and Suppress. People in need of revive or heal are marked on the minimap.
Recon:
+30 additional point per kill for headshot (marksman bonus)
+20 assist points for enemy killed within range of your sensors
+20 additional points for enemy killed in sensor range by squad mate
- Note: added camo, stronger weapons, better unit detection, and the later game demo/mortar abilities make this the class that gets the most points from K:D on top of raking mad points from the spotter bonuses.
Vehicle:
+10 passenger assist for every kill made by someone else in the vehicle (a tank in a good defensive position fully manned with a repair team racks up mad points).
+? additional points for squad passenger assist
Plus the numerous pins and badges. Still a WiP, values subject to change.
The big thing is to pick a role and stick with it. You get pins for doing a certain number of actions a certain number of times (i.e. repair efficiency for 7 repairs in a match), and those pins are all at least 100 points each. I usually get 2 or 3 repair pins in a round, so if you count 3x7repairsx20points/repair+3x100points, that comes out to 720 points. Play your role consistently and play it well, and you'll get rewarded for it. Do so while working with your squad, and you'll receive hefty bonuses for it. Squads with highest scores get best squad pin rewards, and those are pretty nice.
[removed by edit]
It really is good game design, players fall into their respective roles naturally. Still one too many snipers (and you guys aren't any exception, are you?

), but it should even out as people learn the game.
In regards to unlocks:
You have a primary level unlock, and you have unlocks for each of the 5 classes (pilot/driver is considered a class). As you use a class, you get points towards your overall unlock and towards your specific class. The weapons seem to be pretty balanced, so it's more about having alternate options that you can change up as necessary. The starters are more or less garbage though... you're supposed to master the trash before you move up. Once you learn how to kill with the starter, you can play any gun in that class in the game like you were born with it (you're then just choosing which one best suits your fancy). A good method I think, but it might be frustrating to those of us used to the easy kills in MW2.

You should be sporting a couple different weapon options within a specific class before you even hit rank 1. When you do hit rank 1, you get the first shotgun, so that's a definite second option for every class.
In addition to weapons and gear, you have specializations (kinda like perks, but smarter). These just further modify your class setup to gear towards a specific role. You can change any of your equipment at the squad spawn screen (just like any BF game), so you can redefine your role as necessary for the changing conflict. It's actually a really well though out system, one that Whata shouldn't even be able to complain about.
This game is a little bit dumbed down from BF2/BF2142, but it does so while adding in a ton of enhancements. I'd say it's an overall improvement in design, and so far I'm quite happy with it.