How to declutter a dining room table?

You don't say what all it is that is cluttering up your dining room table. Books & papers, clothing? Who is cluttering it up? Whatever it is and whoever is doing it you need change and train. If it is an easy spot to drop something until it gets put away find or make another location that things can be dropped. Train yourself and everyone else that the table isn't it. Use the new place or put it away.

I try to clear my counters and table nightly because it's too big of an issue if I let it build up. I don't bring junk mail into the house and throw it in the trash outside.

You can hold items hostage and make them do chores to get them back.

Baskets William. You can clean off the table and keep everything in large baskets until you need it again. If you are handy you could build a bench with storage inside for things you use regularly at the table. I know my dining room table gets cluttered with computers and papers all the time!

This is a thorny problem for a lot of us. Regarding junk mail, I don't let it get much past the threshold. I open the nearby door to the garage and toss it into the recycling bin right away. I like the idea of using a box to toss stuff into instead of onto a table and then sorting it once a week. I think the important thing is just to avoid keeping stuff of no importance, whatever that may mean for you.

this is a really dumb question.. to de-clutter a dining room table, don't let it get cluttered in the first place! put everything away as soon as the stuff comes in the house. if you pile everything on every available surface, first thing you know you have a hoard and you are a hoarder!