Making the most powerful and fun to play team I can build with perfect IV's, EV's, and Natures. Test the team out many times until I perfect the Strategy. Swap in and out the weaknesses and Strengths. Then when it feels just right, climb your way up the rankings online.
This keeps the game alive for me constantly. Just achieving the perfect pokemon is a long arduous task that takes much time and in it's own way is fun. Practicing with your team gives you all the fun of battling with your team but it also teaches you how to develop strategy, how to make your strategy more efficient, and how to recognize weaknesses in your team.
Then when you think you have it down begin climbing your way through Battle Subway and then Test out your Strategies online.
Let me tell you, I get so much satisfaction and fulfillment when I beat somebody with my prized team online. It just feels so good and fun.
Even if you are not a fan of online play, just start out with the goal, "I'm going to try to develop the best and most efficient team I can build." Try achieving perfect stat pokemon, and trust me, you'll feel closer to the game and you tend to personalize your team more and more until it feels like a pokemon team that is a manifestation of your personality and preferences. Once you achieve that point, all the battling and strategy development falls into line on it's own.
Edit: A tip on how to get started on doing this, find ONE pokemon that you have always liked a lot. Then build the team around that pokemon. For me I chose Gorebyss and the rest of the team fell into place for me.
That's how my experience and fun factor with pokemon works. Hope this helps. :)