Increased weapon damage. In Battlefield 4 the weapon damage is laughable. I think Hardline got it right(28 for most AR-s, 36 for AKM, 43 for Battlerifles).
Every example is a chest hit
SMGs: 3 bullets to kill when the enemy is 50m or closer, 4 from 50-100 and 5 bullets beyond 100 meters.
Semi Auto Rifles: 1 bullet for 10 meters, 2 from 10-75 and 3 beyond 75 meters(if you get a headshot it would be 2x dmg multiplier as in BF3-4-Hardline). But make them kick like a mule to make them in balance with SMG-s
Bolt Action Rifles: 1 bullet for 50 meters, 2 bullets beyond 50 meters and a headshot is always an insta kill.
LMGs: Similar to SMGs but they have increased range in exchange for rate of fire and recoil. 3 bullets for 75m, 4 beyond 75m
Classes: If the rumors are true then no significant change is needed.
Assault has SMG or bolt action+anti tank granades,
Support has LMG/AT Rifle+ammo box and TNT,
Medic has a Semi auto rifle + medbag and adrenaline (WW1 Defibs :D)
Sniper well that is self explenatory.
No engineer? That means vehicles can´t be repaired? It can turn out good and bad too, but I´m sure Dice will figure it out.
Authentic weapon attachments. No red dot sights and Acogs.Don´t make the hand to hand combat QTE based!!!
Teamwork: You should encourage everyone to join a squad and obeying the squad leaders orders. Winning should be the number one priority not your KD. Make a good commorose like it was in BF2, give huge benefits for teamwork (faster leveling up, more unlocks, maybe a badge or something in front of your name, so people will know that you are a good team player) maybe add some perks to the whole team which can be only achieved by teamwork like if you get certain amount of teamwork points with you squad, then your tickets wouldn´t deplete for 2 minutes giving you a chance to gain the lead(which will give you more ponints and unlocks and everything after you win the match). This could be achieved lets say every 20 minutes to prevent games lasting forever. And small things like this to encourage teamwork.
At least as good destruction as it was in BC2.
Vehicles: Not enough info yet.