I was having issues too, and this is what helped me:
take a little nursing vacation -- take your baby to bed with you, and for several days do nothing but relax and nurse your baby
make sure you are taking in plenty of calories -- if you have a small appetite, try throwing some protein bars into your diet -- little snacks that pack a large nutritional punch
eat or drink more dairy -- when you want a small snack, have a glass of milk, a piece of string cheese, or yogurt
drink Mother's Milk tea -- I would make up an entire pitcher and keep it in the fridge, so it was easy to drink one or two glasses a day
When my supply is really down, I take supplements for about three or four days to get it back up again -- I use Solaray Lactation Ease that I get from my local health food store
and most importantly, quit stressing! While I still do everything I can to keep my supply up, I have come to the conclusion that I am just not one of those mommies with gobs of extra milk. I'm just not. My son is eight months old and has always had one or two supplementary bottles of formula every day.
Still nursing my son at 8 months -- He is happy and healthy -- and that's what really matters!