how to build up an attacking, defending, and prestige team

Be on lookout for friendly gyms with Exeggutors and gyarados on the bottom of the gym. They are the best to prestige. Use scythers/parasects/venomoths and jolteons/Raichu with half the cp of the highest of the gym.

Just beat the bottom and run away.

Might as well upgrade your attackers and make them capable of steamrolling enemy gyms to save potions/revives. (If it's poke that's worth investing in)

More and more players are putting double weak Pokemon in gyms lately in my area which is helping a lot with prestige. Hopefully it will catch on! Golem, rhydon, gyarados do have a good use defensively!

Just keep in mind that some Pokemon are only top tier because of their high base stat/max possible CP.

For example: a 1000CP snorlax isn't any better than a 1000CP Wiggly for prestige purposes

When training at an ally gym, if the highest CP in your party is half of the defending pokemon's CP, you gain 500 prestige for defeating the pokemon. If you exactly match the defender's CP, then (I think after the gym nerf) you gain 250 prestige. If you are above the defender's CP, then it quickly drops to only 50 prestige.
- You want pokemon with offensive movesets across a range of CPs. IVs don't really matter since you are not powering them up as high as you can.
- Depending on the size of the pokemon in a gym, I am often selecting a team around 900, 1000, 1100, or 1200CP.
- If there is a big size gap from the first to the second pokemon in a gym, either select your CP only for the first pokemon and run after you beat it, or ignore the CP of the first and resign yourself to getting less prestige for it.

When fighting an enemy gym, you take off a flat 1000 prestige for each pokemon defeated. CP doesn't affect prestige taken, so feel free to use your biggest and strongest pokemon.
- Having a good offensive moveset is most important. If you are attacking by yourself, single use charge moves like Fire Blast are generally better. If you are attacking with a team, multiuse charge moves like Flamethrower can be better since you can use them sooner and more often.
- The attacker naturally has the advantage, especially if you are attacking with a team, so high IVs are not too important, but they do help a little.

When putting a pokemon into a gym, CP directly dictates how high in the gym you will be placed.
- To place as high as possible, especially if you are not as high a level as other players in your area, high IVs are very important. For most pokemon at level 30, the difference between 0% and 100% IVs calculates out to a range of about 300CP, which could greatly affect your placement in a gym. If you are a lower level than other players, but they don't have good IVs, then you could still place higher if you have really good IVs and you power up to your max.
- Defensive movesets generally have quick moves with longer durations. The added 2s cooldown in between attacks changes the DPS calculations, and longer duration quick moves are generally stronger in gyms.
- Although, really, movesets don't matter too much since the gym change. If an attacker decides to take down a gym, they will be able to and you can't stop them. But I figure, I don't have to make it easy on them. (Although, as I think about this, I suppose intentionally putting a pokemon with a bad defensive moveset in would make training up the gym a little easier. Meh.)