I would recommend reading this article on the anaerobic threshold test –
Key items –
– Do a 15-minute warm-up at or below your Aerobic Threshold (AeT) or until you break a sweat. Ease into this warm-up so that your aerobic system is fully online.
– As soon as you are done with the warm-up, continue immediately into the AnT test. Once you start, go as hard as you can sustain for the full 30 minutes.
– Pace yourself so that you don’t blow up 5 minutes into the test.
If you think you could have gone harder, then maybe do another test in a few weeks.