Random dailies give a lot of XP per minute.
Master writs can give huge amounts of XP per minute.
Crafting writs aren't bad.
Saving up quest turnins can be OK depending on how slow your loading screens are going from quest giver to quest giver.
And of course there are grind spots such as dolmens.
I use them when i level up unused skills/morphs in bruma. Town has 10 daily quests that can be done in a few mins each(fastest takes about 30 seconds). Similar with other cyrodiil towns.
Use xp scroll on a character then go into a random to get high xp
When you finish dungeon log out so you are not wastimg the time left onyour scroll...next day do the random daily again. Helps if you have a healer friend or tank if you are dps or if you are tank or healer so you get speedier queues and you dont waste scroll time the next day.
If you are playing on your main then use scroll when you get into the dungeon then after dungeon go do your writs so when you hand them in you can use up that xp scroll that is ticking over...if you still have time go do some world bosses or a public dungeon. Just keep doing stuff that gives xp so you dont waste what is left of your scroll.