One of the key factors in winning a game is
  how you play your opening hand. If you play it efficiently your most likely
  going to get a nice jump on your opponent, but if you don't play it right, you
  allow your opponent the starting advantage. So exactly how do you play
  your opening hand? Just follow these rules and you'll be fine.
   
  1. HOW MANY POKEMON TO PUT DOWN: It's always an important
  factor in how many pokemon you bench. Most of the time it's bad to play all of
  your pokemon because your opponent can take advantage of you not being
  able to power up ALL of your pokemon and GOW out an energy less one
  for an easy KO. The only situations you should play all of your basics is
  if you your playing a stall and if you only drew 1-2 basic pokemon in
  your opening hand. Most of the time it's a good idea to send out an
  active pokemon and a benched so you won't lose because of pokemon
  shortage. 
   
  2. HOW TO CHOOSE POKEMON: If you have a pokemon with free
  retreat ALWAYS send it out as your active. Why? Because you can retreat for
  another one to make sure you have what you need battling. If you don't have a
  free retreat pokemon send out a "Haymaker Pokemon". I'm sure you all
  know what they are, but here's the list anyway.
  GRASS:Scyther(Does not need grass energy)
  WATER:Lapras
  PSYCHIC:Jynx Promo Mewtwo(From the Movie ONLY)
  FIRE: Magmar(Fossil)
  ELECTRIC:Electabuzz(Base Set)
  FIGHTING:Hitmonchan 
  COLORLESS: Farfetch'd
      All of these pokemon are considered
  "Haymaker Pokemon" because of their high Hp and ability to do big
  quick damage. The reason why it's a nice idea to send these guys out is
  because they can hold their own with little energy allowing you to give your
  opponent a heavy beat down while you work on your bench. If you don't have a
  free retreat or Haymaker pokemon it's always a good idea to 
  use a stalling pokemon while you build up your bench so your opponent
  won't get the starting advantage. If none of these pokemon are in your opening
  hand then send out a pokemon you drew doubles of(Ex.If you drew 2 Vulpix,
  and 1 Base Magmar). And if you didn't draw doubles send out a pokemon
  that has a 1 energy attack or you can afford to lose(Ex. Ditto or Squirtle).
   
  3. WHAT NOT TO SEND OUT AS YOUR ACTIVE:
  Never send out ANY pokemon that is a key to the deck(Ex. Squirtle in Rain
  Dace) Also, don't send it out if it has a high retreat and can't
  hold it's own with little energy(Ex. Tangela who has a 2 retreat and needs to
  grass energy for it's lowest attack cost).
   
  4. USE THE METAGAME TO YOUR ADVANTAGE: Send out pokemon
  according to the "metagame". If the "metagame" around your
  area is Rain Dance and you draw 1 Fossil Magmar, and 2 Electabuzz, send
  out an Electabuzz as your active and the other Electabuzz as your benched.
   
  5. HOW TO SEND OUT POKEMON ACCORDING TO ENERGY: You
  need to send out a pokemon that you DON'T have the
  energy to build up (Unless you're playing a Haymaker in which you do send out
  the pokemon you have the energy for) while you build up the one that
  you have the energy to build up. Here is a game where this principal is
  used(Well, kinda) John and Tyler have just drawn there cards and you
  hand is 1 Electabuzz, 1 Fossil Magmar, 1 Fire energy, 1 electric energy, and 1
  Scoop Up(The rest is unnecessary). Who do you send out? Magmar or Electabuzz?
  If you said Magmar you are correct. Let Magmar stall while you build up
  Electabuzz then Scoop Up Magmar allowing your damage free Electabuzz to Thunder
  Punch yourself to victory. Just in case your wondering why I didn't send
  out Electabuzz to begin with it was because Thunder Punch damages
  Electabuzz(Sometimes) so I didn't want damage on him if I flipped tails(I
  had also been having bud luck the past 3 games :-(       
   
      So there you have it! How to play your
  opening hand! Apply this to you game and you'll master the beginning game of pokemon
  in no time at all!
   
  Sincerely,
  ~Tycoon