You need to get a source of ammonia for the bacteria to grow. I use ammonia based cleaner from ACE hardware (ACE brand)--it has no perfumes or any other additives that you won't want in your tank and is quite cheap. You will want a concentration of about 4
ppm according to a test kit. If you go too high, the cycle can stall, but if it's too low, the rate at which the bacteria will multiply will diminish. It will take a bit of time, but gradually that ammonia should be converted into nitrite. Then another bacteria will grow that will consume nitrite and make nitrate. When you reach this stage, you're ready to add fish.
In order to speed things up, you have a few options:
1) Add a product like cycle, although the benefit that it provides has varied.
2) Get an old sponge or filter pad from an established, healthy tank--this is the best option if you can manage it.
3) Add a scoop of gravel from an established, healthy tank--not giving you as much bacteria as the second option, but certainly helps.
