I would stick to straight attacking for the majority of my fights, but sometimes, a little strategy was in order. For example, during my Platinum playthrough, the only strong Pokemon I had was a Level 22 Budew. I got to fight Mars, and she sent out her Purugly that absolutely destroyed me. After a little bit of leveling, I decided to try again with a strategy in mind.
I sent out my Piplup to use Stealth Rock at the start of the fight, then I threw out my HM Slave. It got killed in one hit, but that let me switch into my Budew without losing a turn. I stunned the Zubats with Stun Spore, and proceeded to use Growth six times, Mega Drain the Zubats, and then Stun Spore Purugly and Mega Drain it over and over again.