Recently I was particularly appalled by ds1's table manners when we were attempting to have a civilised meal in a hotel.
Since we got home I have insisted that after every meal ds1 clears away all his crockery (usually did this anyway), then tidies the table, collects up any crumbs and mess, wipes the mats, and the table; THEN gets the dustpan and brush out and sweeps up under his section.
It's worked wonders in just a few days 