Otrivin is the most powerful decongestant available without prescription. It's usually only available from behind the counter at UK pharmacies. But don't use it too much or it will give you persistant rhinitis. Don't use earplugs. Some are advertised as being useful for this purpose. This is rubbish - they will probably be more harmful!
My advice is to chew 'Airwaves' chewing gum. It has menthol which will help open the eustacion tubes while the chewing action will exercise them and allow air into the middle ear. It really works and in over two decades of professional flying, I have found it really is the best method. I never fly without it.
Be careful while re-inflating the middle ear with the valsalva movement (pinching the nose and blowing). Apply too much pressure and you can perforate your eardrum. The voice of experience!