I've just been overly careful, I make sure to fight all the trainers to keep a decent lvl. If a pokemon even has the possibility to learn Either dragon rage or Sonicboom I run away. I do NOT wanna deal with that. I usually don't bother trying to catch Legendaries, I either kill em for the EXP or run if they don't look too friendly. Only exception so far Is the mew in blue and Thats just cause I had a bad luck streak before it. I also dont usually have a balanced team of 6 pokemon till about 4 badges in the game when Im happy with the pokemon I caught. At the beginning I just catch everything I can and Train two pokemon. One of them being the weakness of the 1st gym leader. Other than that it's allot of luck. And I wish you all of it.