Drinking plenty of fluids helps a lot (both water and warm tea). I wake up congested until I've had a glass of water.

Thanks to allergies, I keep nasal decongestant in-stock for immediate relief when it gets too rough.

For extreme cases, or when I eventually get sick of it lasting too long, I have a neti pot (which can be found online - Amazon). They're very weird when you first try them (and you'll learn the proper angle to hold your head very quickly!) But wow, do they work great!