Hawaii Volcanos National Park is one of our favorite parks. Well worth a visit.
As Ken and Dan say, the volcano and its activity changes frequently, so you will want to check the Park Service Website re current conditions. When we were there most recently (this May — usually we go in January, but this year we postponed our visit), the only place you could see lava in the Halema’uma’a Crater in the Kilauea Caldera was from the Keanakako’i Crater. (A 2 mile round trip hike, but mostly on a paved road.) At the other viewing points, you could see orange glow before or after sunset, but not actual lava. And there was no lava flowing into the ocean or along the lava fields from the crater to the coast that Dan mentioned. We have hiked in the area Dan mentioned when there was lava flowing to the ocean in earlier years — pretty spectacular when it happens. We had flashlights and went with a small guided group that hiked in the adjacent state/local park, where there is closer permitted access than in the NP, and stayed until after dark.
I brought my Z6II and the Z 24-120 mm lens to the park. A longer focal length would have been nice (I had my Z 100-400 with me in Hawaii, but did not bring it to the park), at least from the Keanakao’i Crater.
Probably best to see the lava before sunrise (the park rangers told us that this was the least busy time) or after sunset (busier, but the people did thin out after a while). We decided to go after sunset. We were staying on the northwest coast of the Big Island and we did not want to drive back to our hotel from the park after dark. So we booked a night at the Kilauea Lodge in Volcano Village. The village is near the main park entrance. Convenient. Nice restaurant. If you like Thai food, the nearby Thai Thai restaurant is good. There are other places to stay in the village.
There are other interesting things to see and do in the park. If you like to hike, the Kilauea Iki hike is our favorite hike on the Big Island. There are several ways to do the hike. We like to start near the Visitor Center and Volcano House and first descend into the Kilauea Caldera, hike along the edge of the caldera and then out of the caldera to Kilauea Iki. Good to have a park map with you.
The Chain of Craters road down to the ocean is very pretty and worth the drive.
Have a great trip.