Well, my opinion is that Trainer Cards are what makes the game, but there's more to the game than just that.

1]  Choose what type(s) of Pokemon you are going to use:
    You have to limit yourself to (at most) three different types of Pokemon (and maybe soome Colourless cards).  You have to remember that when you have different types, you have to have an ample supply of energy cards to back up each type.  15 is a good amount for one type of energy cards because then you have a 1 to 4 chance of getting the energy you need.
    When you have one type of Pokemon, you don't need as many energy cards, leaving more room for trainers and such, but that means that if you face your  type's weakness, you're doomed.  Two different types of Pokemon are good so that you aren't always at a disadvantage with weakness.  But that means that you need more energy cards to supply enough for both types.
   I believe that the best thing that you can do is get two types that sort of complement each other.  For example, you can focus on Grass type Pokemon and get a couple of Water Pokemon.  This way, you don't need to get a lot of Water energy, just a couple.  And when you face Grass' weakness (Fire) you can take out Fire's weakness and turn the tables around!

2]  Choose your Pokemon wisely:
    This is an obvious one because you can't win without good Pokemon, right?   There are three things that you need to focus on when picking your Pokemon: [1] their HP, [2] the cost of their moves, and [3] the strength and status changes of their moves.
    If I had to pick one good starter, I would say it's Nidoran(female).  She has 60HP(nice), cheap moves and they're all pretty decent moves.  Her "Fury Swipes" are bound to take off at least 10 (3 tails are VERY rare) and her "Call For Family" is useful in the begining of the game.  Other than him, Machop, Krabby and Staryu are good too.
    A stage one that's good is Sandslash.  He has 70HP (real good), cheap moves and they're both decent.  Not only do his moves cost only two energy cards, but he has resistance to electric.  A really good card.
    I don't really care for stage 2 pokemon.  If I put them in my deck, than means that I need to get (while playing) the basic and stage 1 cards before I can then find the stage 2 card, or I have to add some Pokemon Breeder cards.  So, I don't know any good ones (I guess the two most talked about ones [Blastoise and Charizard] are good for their Pokemon Powers...)

3]  Decide of the quantity of each card:
    If you have a trainer that you find is very useful, get more than one of it (like Bill).  If you have a good Pokemon, then get some more of its cards.  If you have a stage 1 Pokemon, get at least 2 of its basic.
    That reminds me, I always make sure than if I have X amount of stage 1 Pokemon, then I get X basic Pokemon and one more.  Example, I have two Seadras, so I keep at least three Horseas in my deck.  But since I don't really care for Horsea, I trade any others that I get.
    But, then again, I have two Kinglers, but four Krabbys.  Why?  Because Kraby's a good starter Pokemon.  So, when I draw my hand, instead of a 1 to 60 chance of getting him, I have a 1 to 15 chance of getting him.  (And don't forget his "Call For Family" move)

4]  Get Traners that work with your deck:
    Well, you just Have to have some Bill cards in your deck (unless you're using a Staller deck...), but other than that, you shouldn't just take good Trainers.  Take those that will help your deck.

    Have to little Energy cards?  --  Get a Energy Search.
    Have some Pokemon that discard energies for moves? --  Get an Energy retrieval.
    Pokemon with high retreat rates?  --  Switches
    Deck focuses on high evolutions?  --  Pokemon Breeder
    Weak Pokemon? Stall deck? Monocolour deck?  --  Potions/Super Potions
    Deck slow to strengthen up?  --  (Super) Energy Removals
    Pokemon harm self when they attack?  --  Defender
    Have one card of good Pokemon?  --  Computer Search

    And there are tons more combinations to your deck.  I also advise a Prof. Oak and a Gust Of Wind.

5]  Practice!!
    I wish that I lived in North America where I could test my deck on some decent Pokemon players.  That way, I'll know what else to add to my deck.  All I did was simply improve my Preconstructed deck.  But I see very few, or even no such decks used in tournament that I've read of down there.  I don't even know why people like Scyther so much!! (But then again, I have Magmar...)
    If you practise, you'll see how each of your cards work in your deck (or don't) and if you need more or less energy and so on.

Direct all e-mail to dstbe@hotmail.com, thank you.