newspaper. rolled up. kill em all.
I live on a farm, and we get loads of flies as a result of the cows. Somehow, i have also developed a real fear for them (i had a couple of really bad nightmares about files a few months ago, and it started from there
), so i now frequently patrol the house, can of RAID in one hand (it is great stuff, kills anything living with wings in seconds, i would go into detail abxout the death - it can't be pleasant - but i won't) and a newspaper in the other (more...humane), ther trick is in the wrist action
. You can also try spraying RAID (or other, inferior anti-flying-insect spray) round the doors and windows, it is meant to deter them, but i am not sure how effective it is.