Summarize the following:
The best way to keep your sangria warm all through the evening is to let it simmer in a slow cooker (or crock pot). You could also allow it to simmer in a large pot or saucepan on the stovetop, if you don’t have a slow cooker. Rather than getting out your stemware, choose mugs for serving hot sangria. Not only will the mugs keep the sangria warmer than thin glasses, they also have a nice handle for holding on to the hot beverage. Hot sangria could potentially crack thin glasses, so avoid using these to serve hot sangria. You want all your spices and flavors to combine nicely, so this is an important step. Though you could simply heat the mixture and serve it, letting it simmer for a bit longer creates a more complex and nuanced flavor. Just be sure to keep the burner or slow cooker on a low setting. A cinnamon stick is the perfect garnish -- and stir stick -- for spicy, hot sangria. Pop 1 in each glass before serving. Add an apple or orange slice to the rim of the glass or pop a few fresh cranberries on top.

Summary:
Serve hot sangria from the stovetop or a slow cooker. Choose heat-resistant glasses for serving hot sangria. Let hot sangria simmer for 20 to 30 minutes before serving. Garnish the drink with fruit and a cinnamon stick.