I second steam. I pour a full kettle of boiling water in a bowl with a dab of Vicks in it then use a large towel over my head and the bowl. I basically create a menthol steam room just for my head.

I also found these pressure points to help open your lower sinuses. If you start at your nose and trace your cheek points, press right before their lowest point and tilt your head back.

A neti pot and sinus rinse is also useful