Sometimes, waffles get soggy when there's too much moisture in or around them. Some recipes call for buttermilk in waffles, which can make the batter heavier and less crispy when cooked. That's why I just recommend using regular milk -- it'll allow the waffles to get a great crispy texture. Also, make sure you don't stack them, which traps steam and can result in soggy waffles. Instead, let them cool and rest on wire racks where plenty of air can escape.