Team Preview was a pretty controversial addition to the game. It can be hard getting used to seeing both teams before each battle, but it can also be used greatly towards your advantage. A little pre-thought before each battle can definitely push the odds in your favor.
Before beginning a match, take a good look at what exactly you're up against. This is the time to create a rough strategy and determine which of your team members are going to be most useful in the match. You'll also want to make a record of your opponent's team to use as a reference throughout the match. The fastest method would be simply to memorize the opposing team. If that's not your cup of tea, try writing it down or taking a picture of the team preview screen with your phone. Just make sure you're always aware of what they have left.
But that's enough talking. To illustrate what I said, I'm going to include three sample team preview screens below. The examples used feature a fairly standard Sand team that I used previously, which means you should know the general sets. Just assume for the purpose of this guide that all sets are the most common ones listed.Take a good look at each picture and think about how you would respond. Then read the commentary below to see if you came up with the same thoughts.
Example 1
Not a bad matchup. I can see right away that I'll want to keep Terrakion alive, as my opponent has no safe switch-ins to it. Virizion could be a bit problematic depending on the set, but Gliscor can handle physical variants and Scizor can take on special sets if it's at high health. Terrakion is aways there to finish it off when it's weakened.
That Kyurem is probably Scarfed, since that's the most common set. To switch into it, I'll want to keep Scizor or Tyranitar alive, preferably both. Scizor is more valuable because it handles other members of his team and because Tyranitar can be hit on the switch with a Focus Blast. Again, Terrakion can check it in a pinch.
Rotom-W is going to be useful this match for handling Heatran and checking Scizor with HP Fire. I can also hit Ferrothorn on the switch with HP Fire for a 2HKO. Similarly, Celebi has a useful role of handling Rotom-W and checking Scizor. It'll become a lot more useful if I can take out his Heatran. Gliscor can switch directly into Scizor, Taunt Ferrothorn to prevent it setting up, and counter Virizion if it's physical. All in all, I can win simply by playing my resistances right and bringing in Terrakion on safe turns to spam Close Combat.
Example 2
Interesting. Celebi won't be sweeping easily in this match, with Snorlax, Victini and Latios standing in the way. Tyranitar can eliminate the latter, but he'll still have some solid switch-ins. Gliscor will be very helpful for switching into Victini, although I have a few other members who can switch into a V-Create. Scizor is going to be helpful for handling Snorlax and Virizion if it's specially-based (otherwise Gliscor will take it on).
Terrakion is also going to have some important usage in this battle. Of his two Fighting resists, one is physically frail and can be taken out by Tyranitar (Latios) and the other is weak to Stealth Rock (Victini). Swampert is quite physically bulky, but it lacks recovery and can't be expected to take Close Combats consistently. I'll definitely want to keep Terrakion alive here. I can see it finishing off his team late-game after Stealth Rock and my attacks have done some damage.
Example 3
Slightly different team this time, but the sets are still pretty self-explanatory. I can safely lead with Tyranitar, considering he doesn't run a different weather starter. Slowbro also hard counters Conkeldurr, so I won't have to worry about that threat. I can definitely see Excadrill sweeping late-game, as he lacks a hard counter to it. Conkeldurr's Mach Punch will take it out, but he can't switch anything in directly without risking a 2HKO after Stealth Rock. Besides, I can always go to Slowbro for Conkeldurr. Excadrill will also check Celebi and Thundurus, meaning I'll definitely want to be sure to keep it safe.
Celebi will be extremely important for countering Jellicent. It can also hit Scizor with HP Fire on a predicted switch. I can't do much to Hydreigon with it, but Tyranitar is a fairly safe switch-in with the Sandstorm boost and I can definitely wear it down over time. Landorus and Scizor may not be too useful. I'm not running U-turn on the former, so his Celebi can counter me if it has Recover. Scizor gets very few opportunities to set up and he has some good checks to it. I'll use these two to switch into possible U-turns. I think I have this handled if I wear him down over the course of the match and bring in Excadrill when his team is considerably weakened.
All of this and a bit more will run through my head before every match. I didn't get to talk about leading, since the screens show what we ended up selecting anyway, but I would recommend picking the team member that has the best matchup against your opponent's default lead while still being able to handle the majority of his other team members. If he has every one of your Pokémon covered, just pick a lead whose counter you can easily deal with. Depending on the situation, you may want to just lead with your weather starter (if it's slower than your opponent's or if your opponent doesn't have one). You can also lead off with a fast Volt Switch / U-turn user to have a safe way of gaining momentum from the beginning of the match.
I hope this encouraged all of you to put some more effort into thinking through Team Preview. As the battle progresses, each of your team members will rise or drop in importance, which will be the subject of a future guide. Prediction is important, but winning is much more about making the "right" decisions, and that comes with solid theorizing.
A common OU example I use is the offensive core of Excadrill / Landorus. The two are pretty similar overall, so they represent what I call "parallel sweepers," or Pokémon that share the same counters. This means that they can apply pressure on opponents until one of them breaks through, particularly if you have a set designed specifically to eliminate a common counter.
One of my favorite sets is Substitute Landorus. Gliscor's the most popular physical wall, so having HP Ice to take it out is helpful. With Gliscor out of the way, both Landorus and Excadrill have a much easier team sweeping teams. Because of this, Landorus and Excadrill have poor defensive synergy but great offensive synergy together.
