If you're used to raiding in 20-person lobbies and just tap furiously for 50 seconds without looking at your phone, you may not even know that you can dodge in Pokemon Go! In addition to tapping, you can swipe left or right, and your Pokemon will perform a dodge as soon as it finishes its previous action. But why bother dodging?
If you only ever raid in 20-person lobbies, dodging is not important. You'll win with sheer numbers, even if you do absolutely nothing. But if you're raiding with just 1 or 2 other people, dodging can be critically important in some matchups.
If you successfully dodge an attack, your Pokemon will take 75% reduced damage from that attack. With consistent dodging, you can drastically extend the time that a Pokemon is alive, which allows them to deal more total damage. In addition, dodging can allow you to avoid relobbying in certain raids, which will make shortmanning that raid much easier, since you don't have to waste time reviving your Pokemon.
Every attack performed by a Raid Boss is preceded by a brief yellow flash. After the yellow flash, you have 0.7 seconds to swipe either left or right.
If you want to dodge more consistently, tap slower. Pokemon Go's combat system features a one-action buffer:
Despite being very useful in some situations, you generally should not dodge everything. Why? Taking 75% reduced damage sounds great on paper, right?
If you're raiding with just 1 or 2 other people, the most important enemy is the 300-second timer, not the Raid Boss itself. Dodging reduces your DPS for 2 reasons, and dodging too much can sometimes be the reason you run out of time on a Raid.