A basic explanation of Equipment! and obviously, the "Improved Equipment" for bonds is way better. Directives are useful but a one off boost. Unless you play Tier X a lot and earn more than 1 a match, its almost a waste. Run Food instead.
Got a tank and you can't decide what to run on it? check out http://www.vbaddict.net/tankstatistics/overall and find your tank on the list and then check out the Equipment tab (its right next to the crew skills tab also mentioned by me )
Gun Laying Drive vs Vertical Stabilizer
Always always always Vert stab. 20% against ALL movement penalties. This means smaller bloom on turret moving, smaller bloom on hull rotation, smaller bloom on the move, Smaller chance of a miss overall. If you aren't running a Vert stab, it should be that you can't equip one. ALL scouts/lights can carry a Vstab now so there's no excuse.
why start at 1.7x when you can start at 1.27x? It's a much tighter reticle and you still beat the GLD to minimum bloom by .3 sec? Obviously both are best but Rammer - Vstab - Optics are the Trifecta.
Gun Laying Drive
10% faster aim in! Generally only useful for snipers and arty. To be used only if a Vstab isn't available AND you are planning to playing a non-peek-a-boom style. Generally not for heavies but sometimes, its what's there.
Binocs vs Coated optics.
Optics over binocs. simple. The sole practical advantage that bincos have is the free swap out. Bincos give you +25% while stationary for 3 seconds, Optics gives you +10% always. Why optics? because unless you are a TD/SPG/stationary tank with a decent spotting range doing you own spots (like you solo holding a side), you aren't going to be sitting still for very long and if you are like most TD's (not the UDES and above), you are going to have to shift your hull occasionally for shots, which breaks the bonus. Your 'on the move' spotting is the spotting that counts the most in almost every game situation. Whether on initial deployment, or you vs 3 of them in a last stand, chances are you will not be sitting still for long no matter what. The extra 30 yards of spotting on the move can save your life. TL;DR: Binocs when Kemp Boosh!
+5% to all crew skills. Only for closed top turrets sadly, but this does stack with BIA and food! Due to the math, it gets figured in as a 2.2% overall increase in direct skill efficiency. (not to be sneezed at!)
10% faster shell loading times. sadly not for autoloaders. Does what it says on the box . more pew pew, always a good idea! Generally a #1 slot pick
Now, class specific equip loads and uses:
Vstab/GLD - Rammer - Vents. Optics are less a concern here but they have their place in high base VR heavies (T-10, etc)
Vents - Rammer - Optics. This is less a rule of thumb than the other classes. Meds are a widely varied class and the equipment needed varies between vstab/rammer/optics and gld/vents/rammer and can even vary from gun to gun on a single tank. (This still holds true for the Itallian auto-reloaders)
GLD - Rammer - Vents/binocs (especially for the swede TDs)
Rammer (or vents) - Optics - VStab (for autoloaders or single shot)
Vents - Optics/Binocs - camo net (for certain personal missions)
GLD - Rammer - Camo net.... Chemo therapy.... (I kid, I kid)
Binocs are a viable option on this class in certain SPGs with good base VR and the potential for clutch shots (like Clan wars)
It's worth pointing out that if you are self spotting a target, even if it was initially spotted by someone else, will help to maximize your Exp. Since radio spotting for your dmg splits the EXP between you and the spotter. If you can see it "yourself" you get more exp for hurting it.