There are a lot of things that go into the rock hard buds that people post pictures of. First off what strains are you growing? Genetics have a lot to do with the quality of buds you get. Autoflowers tend to have less dense buds so that might be an issue. Finally, the lights you are using and how far away from the plants can significantly effect bud density. I suggest going to growweedeasy.com and doing some research on growing and I bet you will be posting some rock hard nuggets in no time!