See this chart this chart tells all of the natures.
What is Ev Training?
Ev Training are attributes which give bonuses to a Pokémon's stats and improve differently depending which Pokémon they defeat. These bonuses, in the form of effort points, are gained in addition to bonuses gained by increasing level.Each Pokemon gets a maximum of 510 EV's. But since this number is not divisible by 4, there are two EV's that will be unused when you complete your training.
How to EV train:
To begin EV training a Pokemon, it is recommended you use a Pokemon that has not received experience from any battles yet, in other words it is best to breed the Pokemon you want to EV train or trade for a UT, or untouched, Pokemon. This way the Pokemon you are training gets the maximum amount of EV points in the stats you want after the training. It is also a good idea to level your Pokemon up to level 15 or so using Rare Candies or the Daycare as these methods of level up will not give you EV points. After you have your Pokemon ready using the steps I have provided, you can EV train for the best results! Another piece of advice I recommend is to give stat building items to your Pokemon, such as protein, carbos, calcium, etc, etc... You can give up to ten of each item to a stat of a Pokemon. Each stat building item you give takes away ten EV points, so be careful which items you use to increase the stats of your Pokemon.
EV training with Items and Pokerus:
Another thing to take into consideration is Pokerus, which is a disease that doubles the amount of EV points your Pokemon receives per battle. Pokerus can be found through a random encounter with a wild Pokemon, although it is extremely rare. Pokerus can be identified by checking your Pokemon for a purple sign that reads "PKRS" in your Pokemon's description, or by the nurse at the Pokecenter informing you that your Pokemon has become infected with Pokerus. After a while, the purple PKRS notice on your Pokemon's description will disappear and be replaced by a yellow smiley face in your Pokemon's description. The yellow smiley face symbolizes that your Pokemon is still reaping the benefits of the Pokerus, but no longer can spread Pokerus to other Pokemon in your party. If you want one of your Pokemon that is contagious with Pokerus to stay contagious, you can store it in your PC and bring it out to infect other Pokemon as necessary.
Items that increase the amount of EV's you receive per battle:
Power Weight - Adds 4 HP EVs to the amount gained after each battle
Power Bracer - Adds 4 Attack Evs to the amount gained after each battle
Power Belt - Adds 4 Defense EVs to the amount gained after each battle
Power Lens - Adds 4 Special Attack EVs to the amount gained after each battle
Power Band - Adds 4 Special Defense EVs to the amount gained after each battle
Power Anklet - Adds 4 Speed EVs to the amount gained after each battle
Macho Brace - Double the mount of Evs gained after each battle
It should also be noted that Pokerus can compound the affects of the Power Items and Macho Brace, so instead of getting only four EV points in a battle using a power item, when used in partnership with Pokerus you can reap a maximum of 8 EV points per battle.
Where to Ev Train in B/W
HP: Driftveil Bridge - Duckett/ Stunfisk - Route 8/ Moor of Icirrus
Attack : Route 1 - Patrat/Lillipup
Defense: Pinwheel Forest - Sweedle/ Venipede
Sp.Attack: Celestial Tower - Litwick
Sp.Defense: Route 4,7,18 Driftveil City, P2 Lab - Frillish
Speed: Route 1,3,6,11,14. Striaton City, Wellspring, Pinwheel Forest, Dragonspiral Tower, Victory Road, Gaint Chasm, Abundant Shrine. Losthorn Forest - Basculin