1) If you plan to do this in the evening , bring some flashlights, some sort of map that you can follow on your way back and first aid kit.
2) It is advised that people with respiratory problems or heart problems, pregnant women, infants, and elderly people do not attempt this hike as volcanic fumes can be really hazardous to health.
3) No one can predict lava flow and lava viewing conditions change daily. Often a 1+ hour hike over hazardous terrain is necessary to reach the flow front of the lava. That is one of the prime reasons why I will advise to go in a guided tour. Guides are well trained and they always know how much walking is required to get to the lava surface flow.
4) I was surprised to see the texture of the lava field . It was like walking on very thin , broken pieces of glass. So you can imagine the importance of wearing sturdy shoes. People often wear flip-flops or sandals and get injured by small fine glass like material that gets stuck with the exposed skin and bruises it .
5)Above all , maintain the sanctity of the place. Hawaiians have a strong belief in the Goddess of Fire , Pele and they consider it insulting if you throw things in molten lava for fun sake. I think it goes without saying that be respectful and bow to the power of Pele.