As with any part of playing the Elder Scrolls Online, you can do what you want and play how you want. If you have the opportunity to pick up a scroll, then you can do so. If you want to ensure that the scroll makes it out safely, then you should consider whether to pick it up or leave it for someone who is built to do so. Running scrolls can be a lot of fun or very boring, and I do suggest that everyone try to run one at least once to get the experience. There is unfortunately no achievement for capping a scroll, so it likely won’t make much of a difference to most players.
Running builds have a few base requirements. The runner should have capped speed at 200%. This requires the Celerity CP, all three gold jewellery with the Swift trait, sources of Major and Minor Expedition, reasonably high resource regeneration, the ring of the Wild Hunt (15% speed while in combat and 45% while out of combat), and being a Wood Elf for the racial speed passive helps. Some runnings sprint while running, whereas my preference is to maintain buffs and keep 195% speed without sprinting while in combat. This leaves more stamina for roll dodging as needed. A 1-handed weapon and Shield allows the runner to use the reflect ultimate, and cast Defensive Stance with the Asylum weapons (recovering Magicka every few seconds).
A runner won’t do any damage, their role requires that they move quickly and survive, so most of their skills will be buffs and self-heals, possibly some crowd control or snares for opponents chasing them.
While running a scroll, always play as if there’s a full faction stack chasing you. Keep your buffs up, re-cast your HoTs before they fall off, use line of sight as much as possible, and roll dodge whenever going over uneven terrain so you don’t slow down while dropping. Block for the half second to prevent CC when a meteor is going to hit you or when an Agony pull would displace you, and keep moving! A runner who is running and following these basics will be very hard to kill.
If you’re supporting a runner, your role is to keep opponents off of them. Don’t stand too close to the runner so you don’t accidentally blow them up from a bomb, but do try to keep yourself between them and opponents so that they can’t be single targeted. If you’re mounted and there are NPCs (wolves, bandits, etc.) in the area, run through them and pull them so that they don’t put the runner in combat (and slow them down). If you have a pull or knock back skill, or a hard cc skill, use them liberally to keep opponents away from the runner. There’s no shame in dying to keep the runner alive. When you die, just rez up ahead of the runner and then ride back to them so you can continue supporting them.
When one faction is missing their own scroll of one type (offensive or defensive), they are unable to pick up an opposing faction’s scroll of that same type. This makes it reasonable for a faction to cap a scroll of one type in the trii-keep that is in front of their own scroll of that same type.
Scrolls should be placed such that the runner will have to cross more challenging terrain or longer paths in order to escape. For example, AD would place a DC scroll at Bloodmayne but not Blackboot, and an EP scroll at Blackboot but not Bloodmayne. DC would place an AD scroll in Warden but not Rayles, and an EP scroll in Rayles but not Warden. EP would place an AD scroll at Kingscrest but not Farragut, and a DC scroll at Farragut but not Kingscrest. The longest runs would be to place an AD scroll at Dragonclaw, a DC scroll at Drakelowe, and an EP scroll at Brindle.
Sometimes it is in a faction’s interest to place a scroll in less-optimal locations. A DC scroll at Alessia may entice EP to start a great fight, or any scroll in a centre prime keep (Faregyl, Arrius, or Glademist) will usually cause a huge fight. During the Mayhem event, these are the fights you probably want, but outside the double-AP events it is usually not the best move to put your tri-keeps at risk.
Considering the above, every time a scroll is taken from an opponent, it’s the runner’s (or their group leader’s) choice as to where to place the scroll. There are good and bad locations depending on the goals that the runner, their group, or their faction prioritize.
Dunking a scroll means dropping it into the slaughter fish so that nobody can pick it up. When this happens, the scroll will reset after five minutes. If the keep where it was picked up is owned by its home faction, the scroll will reset there. If the keep has flipped and is owned by an opposing faction, then the scroll will reset to a (mostly) random home keep owned by the faction whose home keep it was taken from. If there’s no free keep for the scroll to reset to (due to the faction in question not owning their home keeps, or scrolls already being capped in the keeps that they do own, the scroll will remain in the water until a keep is taken.
For example, the AD scroll of Mnem is being held in Chalman (a red home keep). EP have been pushed back to their tri-keeps (Arrius, Kingscrest, and Farragut). A DC player picks up the scroll of Mnem from Chalman, and drops it in the water. After 5 minutes, the scroll of Mnem will reset to one of the three home keeps that EP have. If in that 5 minutes the EP faction manage to recover Chalman, then the scroll of Mnem would reset back to Chalman.
Some people love running scrolls, some people find it boring and tedious. When your faction has their own scrolls, they get small bonuses to their offence and defence, so it is in everyone’s interest to recover them when they’re lost. I prefer leaving scroll running to those who are built to do so – something I enjoy when solo.