As Creepy_Steve has said, it's all about the trichomes, pistils and density... but weed can throw you a curve ball... I've had some grows where the trichs never did start to turn amber... but the smoke was terrific... (grab a microscope, jeweler's loupe or just zoom in with your camera as far as you can and then zoom the resulting pic). Density isn't a really good measure - again, lots of variation in density depending on the strain and how well the plant was grown. Pistils are a good indicator if all else fails... them AND seeing a good fade going on with your plant....
Good luck - and congrats!