I sometimes find it more difficult at the start of a trip as well I generally attribute it to mild congestion brought on by exposure to different pollen, dry air from the hotel room ac, etc. once I have acclimated, it generally clears up.
It generally helps if I pre-equalize just before I begin my descent, and then I take it nice and slow in a head up position through the first 20 to 30 feet. I also find that if one ear is having more problems, then tilting my head so that ear is higher also helps (tilting your head elongates the Eustachian tube and makes it easier to open).
Check out this article from DAN that includes a few different techniques that you can try: