It’s time to answer that perennial question: what makes a good team? This question can be interpreted into two sections: what makes a balanced team, or what makes an effective team? The principle of a good team in all situations is to have Pokemon of different types that cover each other. It is very hard to win a battle with Pokemon that all have the same weaknesses. A balanced team has Pokemon that support each other. If you are going to have slow and powerful Pokemon, make sure that each member has good defensive abilities and can attack Pokemon of all types. If you have two Pokemon of the same type on the field, they are both susceptible to the same kind of move, making them vulnerable to those attacks. Rather, them with moves that can cover its weaknesses, or switch out one of them. If this is your last resort, try teaming up on the Pokemon that yours are weak to, and take out the threat before it does any more damage.
If you are going to build a fast team, make sure your offensive abilities are top-notch; usually, Pokemon that rely on speed are fairly easy to take out. There’s not really a solution besides taking out the same types, but EV training will maximize their potential. However, a really balanced team is comprised of fast, slow, powerful and defensive Pokemon. Let’s take my White team as an example. My lineup consisted of Serperior, which was very defensive (and fast), Swanna, which was offensive and fast, Simipour, which was offensive, Stoutland, who was slow-moving but powerful, Zebstrika, lightning-fast (get it?) and skilled with attacking quickly, and Cinccino, who was very weak at defense, but could knock out others easily. You can see that 5 out of 6 of my Pokemon were fast and had good offensive abilities. That’s not what I was aiming for, but they have the advantage, since they all have good offensive and speed abilities.
If you want to take hits, putting on hold items is a great idea too. I placed the Rocky Helmet on Stoutland, since it had a very high Defense stat. This would damage anyone who would try to attempt a physical attack on it. Recently, I gave the Big Root to Serperior, since half of its moves steal HP from the target (Leech Seed and Giga Drain). Planning moves is just as important as a stable and sturdy team. Cinccino had Wake-Up Slap, which would cover its Normal ineffectiveness against Rock- and Steel-types. Simipour had Acrobatics, which would cover against Grass-types. In terms of status afflictions, most Pokemon can learn Toxic, but planning for other conditions won’t be very easy. Covering weaknesses is also a very skillful strategy. Electric-types can hold a berry which weakens supereffective Ground-type attacks, since it is their only weakness, and so on. So keep trying and putting your faith in your Pokemon, and strive to be a Pokemon master!