Sorry if this isn't that great a help to you, my knowledge is of the first nine sets. Beyond that, it's mainly just guesswork. So I'll discuss some strategies I see with the Grass type cards in the first three Black and White sets, a stratgey I see with two of the Psychic cards in these sets, then about some deck designs of old.
Okay, in the Grass decks I see two main cards. First is the Royal Heal Serperior (Leaf Storm Serperior is great, but it's pretty basic. You should know what to do with it. Although you can team it up with Reuniculus to spread the damage out and then heal it from your Grass types.) Royal Heal Serperior teamed up with this Bouffalant make for a great pair http://serebii.net/card/blackwhite/091.shtml
The second card I see is Nature Power Sawsbuck. This card when teamed with Leaf Tornado Serperior and Helping Hand Whimsicott can quickly do some damage.
These two things might not seem like strategy, but it is as close as you can get in these times of "HIT EVERYTHING AS HARD AS YOU CAN". Strategy has become obselete.
Or has it? I'm noticing a great combo among the Psychic type cards (of course. Even back in the old days Psychic types were the combo Pokemon.)
This involves using Reuniculus's Damage Swap to put Damage Counters on a Pokemon with high HP. Then, you use the Noble Victories Cofagrigus's Damagriiigus attack to remove all those damage counters and put them on the foe. It heals you and likely KOs the foe (as long as the foe is a basic or Stage 1.)
Okay, now for some old style deck designs.
First off is Haymaker. Haymaker decks use a lot of high hit point basics with an attack that hits hard for just one energy. They're very easy to use but still are very effective and about the biggest danger you could face at times during the early play. They use Trainer cards to control the game. Pretty much, the game has just become one big Haymaker now.
Next is Wigglytuff. This Pokemon from the Jungle set had an awesome Do the Wave attack. This could do up to 60 damage with a full bench. So Wigglytuff was teamed with the Haymaker Pokemon, who as basics could provide nice bench support. This was an easy deck to use and Wigglytuff was the most feared Pokemon until Neo came and Sprout Tower was introduced, lowering Wigglytuff's power to a mear 30.
Next is perhaps one of the most danagerous decks. Rain Dance. It used Blastoise's Rain Dance ability to place as many energies on heavy Water types such as Lapras, Dewgong, Gyarados, Articuno, and Misty's Poliwhirl. It had a ton of card drawing, using four Prof Oak and four Bills. It took a hit in the Gym series with the introduction of Rocket's Zapdos, which hit Water hard along with Electabuzz. Neo came in and saved the day with Wooper, which completely stalls out Zapdos and Electabuzz. It also introduced Feraligatr, which helped stop Rain Dance from decking itself.
Gengar and Mr. Mime were a popular duo. Gengar would move damage counters onto the foe, and Mr. Mime would hit harder the more damage the foe had taken. These two Pokemon could be seen in almost every Psychic deck.
Potpourri was one of the more interesting decks used. It played a bit like Haymaker and usually used the core trio of Haymaker, although it made more use of Colorless Pokemon. It pretty much had every type of Pokemon in the deck, so it could handle any deck thrown at it. It obviously made great use of the Rainbow Energy.
Wildfire is named after the attack of Fossil Moltres, which could be used to deck the foe. Stall was a legitamate strategy starting with Fossil. Using cards like Imposter Prof Oak and Magmar, you could easily stall out the foe and burn through their deck with Moltres. It got to the point that Lass and Gambler were being used to stop Wildfire from winning. These decks became a bit outdated as Wigglytuff and zapdos took centerstage, but they resurged when new stall cards such as Miltank were added to the game in Neo.
No-Energy Stall was considered the hardest deck to use. It involved having no energies in your deck, and using Alakazam's ability to get rid of damage. And speaking of which...
Damage Swap was my personal favorite back in the days. Alakazam would use its ability and spread out the damage counters to be gotten rid of in different ways. I used Chansey and Scoop Up/Pokemon Center, Tentacools (who could be brought back into your hand, taking two damage counters with them), Erika's Clefable, and Sabrina's Golduck. Alakazam was one of the best Pokemon in the old days and could do a lot with Damage Swap. Also, Kadabra was the Pokemon of choice for anti-Haymaker, as it KOd Hitmonchan in one hit and Electabuzz and Scyther in two, then healing off damage with Recover.
Movie Promo Mewtwo was a popular card and for good reason. It was a big anti-removal Pokemon. Its attack let it attach to itself two energy in the discard pile. It was used along with Prof Oak, Computer Search, and item FInder to get Energy in the discard pile. You could easily use Pokemon Center or Scoop Up on it to heal it up, then send it out and get more energies. Along with Mr. Fuji it could be used to prevent decking.
Active Stall was a more offensive version of standard stall. It was better equipped to dealing with Rain Dance and Haymaker, decks that hit too fast for stall to normally be effective. While for expert players, it is still an effective strategy.
Energy Removal. These were in my opinion the best cards in the game. SER was the most feared card in the entire game. In fact, when I feel like playing against some of these new-fangled decks, I still destroy everything with Super Energy Removal. It's one of the best cards in the game. Later, cards like Dark Muk were added to make more Energy Removal cards. Although Energy Removal did take a huge hit when Ecogym was introduced in Neo, uit was still an incredibly viable card.
Finally, the best way to deck your opponent is using 4 Base set Mewtwo and 56 Psychic Energy. Your opponent would have drawn a lot of cards from the mulligan, then when you finally get Mewtwo, you could just keep on using Barrier to stall out the foe. Invincible, at least back then.
