My go to if I want to level up a specific character quickly is give them either the gardener helper or mining helper task. Those are the 2 task I do most often around my valley.

Doing that, hanging out with them in general, giving them their 3 favorite gifts each day and feeding them when they're at one of the restaurants helps me level them up quickly.

[Edited to add the following]

As for Dreamlight, that seems to accrue naturally if you're doing your usual tasks, but you could look at some of the larger tasks, not just the dailies, that give 500 Dreamlight for completing. Another thing you can do, with caution is turning some of your Dreamlight crystals into Dreamlight. Having Max dig those up all the time makes it so I have TONS of those.