Let me start off by saying that there seems to be four different contributing factors to winning a Pokemon match. The first is teambuilding, second choosing the Pokemon you want to use, third is how you play the mons at your disposal, and fourth is luck or hax. In this discussion I will be focusing on the second aspect of a battle, or picking the Pokemon and what order you want them to battle.
Now I consider myself a better-than-average team builder and a fair battler. Granted, I'm definitely not in the top portion of battlers that have been at it for more years than I (Madison regional was my first live tournament) such as the admins of the site, Cybertron, Wolfey, or to be frank most people that haven't joined the site within the past year or so. However, more recently it seems that I'm losing a ton of battles not because of my team, but because I just don't know how to choose what Pokemon to use. Right off the bat I'm at a disadvantage because the type matchups don't go in my favor. Whatever I lead, the opponent leads the perfect counters. Whatever I have in the back, the opponent is prepared for and ready to handle.
I can't identify which of my opponents's Pokemon threaten my team the most, whereas on the flip side the opponent seems to always know what to bring and where to put each Pokemon.
So if I had to make this post into one question (which I could've done in retrospect) it would be this: how do you figure out which Pokemon to lead, and which to bring in back? Is it a mental checklist you go through? A quick scan of the team archetype? Use mons that have the most resistances to the opponent's team? Or do you just have everything countered in teambuilding so well that it doesn't matter what you lead? (partially kidding on the last one)
So I'll open the floor up, excited to see what everyone has to say!