I have terrible allergies almost year round. What works for me is never go outside and avoid all house work, dusting, sweeping etc. : ) kidding of course. (sort of)

I've found that should I need to do things that I know will cause an allergic reaction like mowing the grass. I will breath slow and relaxed without flaring my nostrils or breath in through my mouth and out my nose. Breathing in through your mouth isn't exactly good for your lungs but its often better then a snotty nose. If you do get snotty, the worst thing you can do is blow your nose with force. If you have to blow do it extremely gently. Snorting it back up is better then blowing too hard. Snorting is another thing I try to avoid. The hairs in your nose are like a filter if you snort you're essentially bypassing this filter or taking the junk that is caught there further in. One last suggestion is don't rub your nose , this will just aggravate things and make it worse. All that pollen and dander in your nose filter is just getting smashed into the lining of your nose and will just cause a worse reaction.

That's it for my completely unscientific but experiencially supported suggestions.

And one I havn't tried, for a stuffy nose, that might work:
Clear your sinuses in 20 seconds with accupressure