BE90 pilot conducting an RNAV approach descended below the FAF altitude and received a terrain warning.

Narrative

I was flying into ZZZ airport at night for the first time. I wanted to do the instrument approach to make sure that I cleared terrain on the way in; and also to practice flying the non-precision approaches in the C90; because it had been a while since I had done an approach; and I wanted to practice the procedures; which are a little different in the C90 than other airplanes I have flown. This is an older model C90. I was cleared for the RNAV runway XX approach; and; since I had the airport in sight; I cancelled IFR. I passed ZZZZZ [intersection]; and descended to 8900. Outside of ZZZZZ1; I started descending to 8000 instead of 8700. I'm not sure why I selected 8000. I may have looked at the approach chart wrong. I still had the runway in sight; and it felt low; but I thought the approach was just bringing me in low. I flew it as a 'dive and drive'. I got a Terrain Alert and immediately did the recovery maneuver. The radar altimeter showed 700' AGL at its lowest point. I flew back up to the VNAV glide path and continued the approach; and landed at ZZZ.Cross check v-path with minimum altitudes on the non-precision approaches. Stay on v-path and verify you are at or above minimum altitudes instead of diving and driving. I think fatigue played a large role in this incident; even though I didn't recognize it at the time.