First of all, you have look up from the bottom of the volcano to see if there are any clouds obscuring the peak. If there are, then visibility is a few hundred feet at best on top. It may also be raining on top. Go to the beach and snorkel. If the clouds are minimal, drive up early in the morning.
Take your time driving up. Stop a few places. Enjoy the drive through the ranchland. This will help you acclimate to the elevation. Take your time driving down, too. Use a low gear. In both directions, watch out for the bike riders.
Take layers of clothes and a snack or lunch for day hikes. I hiked down with all my layers. I had a long sleeve shirt, a fleece jacket, and a gortex rain jacket. The wind can be icy-cold and the sun can be very hot. Make sure you have a hat, light gloves, sunglasses, and camera.
The multi-color lava is great. The path down to Ka Lu u o ka Oo crater is something a person who walks regularly can do. Just take your time and rest on the way up. The path is soft sand and gravel. I found that hiking boots were not necessary. I hiked just past Pu u o Pele (See the map at this website). I was scuba diving the next day, so I did not go any farther.
I drove up the volcano twice, but I only did one day of hiking. The first day I drove up, the clouds covered the top. I hiked early in the week and went scuba diving later in the week. After diving, I could not go back up to that elevation to hike. I hate to say that I was disappointed because I did not get to hike more than one day. I was diving instead! But I do hope I get to return to hike more.