Just saw this and thought it helpful:
Gamespur Article: Battlefield 4: Tons of Little Known Tips And Tricks That Players Should Use [gamepur.com] -
By Sehran Sun, 2013-11-03 14:45
Here is massive list of little known tips and tricks that players should used to get upper hand in Battlefield 4 against enemy.
* Pressing E on a dead soldier when medic will automatically switch you to the defibrellator paddles and revive (brings back weapon after revive). - CryptiKau
* Shoot once and don't reload in the LAV to get an extra 12 rounds to regenerate in your ammo pool. - kahoona
* Press F5 and F6 on the attack boat to eject in a jet ski! - 1ildevil
* You can repair reactive armor... You use the repair tool on the side where the reactive armor has been blown off, and eventually the armor will reappear. (or) you may need to repair the vehicle past 100% - rdmx & Zapatopi
* F switches weapons in vehicles/boats. - Zeigy
* In BF4, you can't suffer from reload syndrome because every magazine you reload subtracts from your total ammo. If you noticed you run out of ammo so fast in BF4, that's why.
* Mouse over enemy and hit Q to spot
* Double tap WW to run and you don't have to hold the shift key. Or set your sprint key to auto sprint, so that you don't have to hold any buttons
* There is a brand new cover mechanic that is explained very briefly in the first campaign mission. If you are crouched behind a bipod friendly cover object, you can just use the right mouse button to quickly peak your weapon over it in the ready position. Its much faster than toggling crouch and best yet is that you can center your reticle before hand to put a bead on a target very quickly.
* This is a no brainer that I missed some how. No more running around your starting area racing people for a chance to get into a vehicle. If you want a certain one, just wait in the deploy map before hitting deploy and click on the vehicle icon of what you want, you will spawn right in the drivers seat if its blue. You can also click on the grey icons to see what is available for use on that particular map.
* There is no compass in Hardcore modes, but if you look at the map early on and find the direction of the farthest objective, its much easier to discern location information via radio. When I hear there is a baddy to the west I just look for Objective C for instance via my UI, which I knew was East and do an about face.
* When you see "heavy enemy presence nearby" that's your commander telling you a cruise missle is about to drop on you. Run like hell.
* Call out objectives for your squad as a squadleader. Everyone gets more points / push if you have the objective marked. Everyone gets bonuses for following the order & killing people along the way. Roughly 200+ score per minute.
* You can actually hold a grenade with the pin pulled indefinitely. You can even put it away (without blowing your face off) by switching weapons while you have the pin pulled. Simply press the grenade throw button and then hold the fire button once the animation starts. Your soldier will stick his hand out like he's posing for the Highsman. Jumping will cause you to throw it, but having the pin pulled decreases the time needed to throw, although sprint is disabled.
* Also, this creates a dead man grenade as it drops at your feet if you die. Good for holding points or M-COMs.
* Accept orders given by the commander, even if you don't follow them. It makes for free points for both of you.
* Crouch while swimming and you will dive.
* The AK-12 and its carbine variant AKU-12 both have an increased RoF in burst fire mode.
* If your solider is "angled" behind cover, you can just press on the aim button (ADS) and it'll automatically "aim out" at your target. You can un-ADS to get back into cover. All of this without using your WASD (or moving) keys.
* Tap fire with belt-fed LMGs. Pretty much just 2-3 round bursts will help engage enemies at medium to long range.
* If you are out of rounds while using the mortar, just press and hold E to pick it up and re-deploy, your mortar will go back to full ammo.
* If you have an XP boost active while playing commander, you'll get the boost points but no time will be taken from the boosts duration.
* When you are a squadleader (star behind your name), you have the ability to command your squadmates to either defend or attack by looking at an objective and pressing 'Q'.
* On the deployment screen, double click a spawn point instead of having to press the deploy button.
* Flying choppers over areas can blow up dust to give cover to your guys capping points.
* you can zero your sniper rifle and DRM. This means adjusting your crosshair to a specific distance with bullet drop. Use the PLD and aim at your target to measure distance (RNG = range). Then press V (default key) with your sniper rifle, to configure the range of the shot.
* Double click on a tank to auto spawn, but realize you've forgotten to equip the repair tool? Click your gadget slot and you'll go to the equipment screen, take your time and get your repair tool out, and once you click deploy you'll auto spawn into the tank
* USAS-12 + frags battle pickup is the only super weapon in the game that can be resupplied with ammunition.