While you might think you're helping your server out by stacking all the dirty dishes at the end of the meal, it's important to know that some restaurants don't allow their staff to carry stacked dishes for various reasons. The best thing you can do is place your silverware on the plate, and wait 'til the server comes to collect it. Also, you can neatly fold your napkin on the table, so it won't get dirtier from any leftover sauces and crumbs on your plate.