I'll chip in a few,to unlock shotguns you must use the support class until they unlock. Same goes for DMR rifles,you unlock them by using recon. Carbines are unlocked by using engineer class.
Use Battlelog on the PC/phone/tablet to track unlocks easier for assignments and battle packs
When you unlock XP bonuses in battle packs you must activate them in the options menu.
Attachments make a huge difference on guns. Stability vs accuracy. I prefer stability.
Throw down medic and ammo packs often. It's easy and free XP
Use the spot feature. Right bumper on PS4. Helps your team and gives you easy XP.