Keep your pokemon alive, heal it regularly, walk around with it (if using soul silver or heart gold), take it on walks if using D/P, feed it poffins more regularly if possible, give it a soothbell or any hold item that benefits it, don't use an exp.share - travel back to low level pokemon and train it (without it dieing), massage your pokemon in the city with the electric gym (D/P) you need to rock climb somewhere in the east of the city, massage your pokemon in the tunnel where you dress up your pokemon (soul silver/heart gold).