"Mulled wine is a seasonal staple but although it's easy to make it's also easy to spoil.
You can mull white wine but most people prefer a red. It needs to be inexpensive, obviously, but that doesn’t mean it should be undrinkable so don’t just chuck in the tail ends of bottles you may have hanging round the kitchen. And you don’t want a wine that’s too heavily oaked though that’s relatively unlikely if it’s cheap.
There’s a fair amount of inexpensive own-label Corbières I’ve noticed lately which would fit the bill perfectly or try a basic Portuguese red. Most recipes add water as well which brings down the cost and stops guests getting too plastered but adjust the amount to the strength of your wine.
Whole spices work better than ground ones otherwise you can get an unpleasant powdery sensation as you drink. Cinnamon is probably the most popular spice but you could also use cloves, cardamom (lightly crush a few pods) ginger and nutmeg. Some recommend star anise but use sparingly if you don't want your mulled wine to taste of aniseed.
Most recipes call for sugar but you might want to add a little less than they suggest if your wine is particularly soft and fruity or if you add port."
Personally, I am very fond of cinnamon in my mulled wines at Christmas time.