I have been having problems with the quality of my home-made brew because it always seem to come out flat. I was told to check the quantity of priming sugar, which I did, but it didn't seem to help.
There are a couple of different factors that could be contributing to your problem. My first thought is the priming sugar, so make sure to double check that you are using what the recipe calls for. If that is all good there are a few other possibilities:
Type of yeast and temperature: If you are trying to make an Ale, and you have the bottles down in your cold basement, it may just take a really long time to carbonate. You need warmer climate for those yeast to get the job done.
Type of caps: are you using twist on or clamp on? if you're using twist on maybe they're not getting tight enough to seal in the CO2.
Time between fermenting and bottling: If you wait too long between the time the beer is done fermenting and actually bottling it, a lot of the yeast may have settled down and won't be as active.
Try looking at a few of the bottles that you recently made. if you see the yeast settling down at the bottom, try turning it and rolling it around to re activate the yeast and see if those bottles are in better shape after another week. If you are making an ale, make sure they are not in a cold environment.