Hveragerthi
First thing is to make sure you stay hydrated. If you do not drink enough water the mucous can become too dry making it impossible to cough it up.
Herbs like cayenne and fenugreek are great for thinning out the mucous.
Osha' root is a great expectorant.
If there is a sinus infection then this will have to be addressed as well, but most sinus infections are fungal and are very difficult to get rid of.