Don't know your likes or dislikes, but can suggest tours I took off the Wind which we enjoyed.
Maui- We took a Cata meran sail /snorkel cruise to Lanai. Nice sailing and great snorkelling. We also took a half day tour to Iao Valley and Maui plantation. On your own you can do snorkelling at Molokini , Old Lahaina Luau , Maui Ocean Center amoung other things.
Kuai. We took an all day tour that did Waimea Canyon, toured most of the islands sites
and thought it was quite worthwhile.
Kona- We did a zodiac snorkel tour that went to Cook's Bay . Great snorkelling and the boat ride was thrilling.
Hilo - we did an all day "eco" tour that did orchid farm, Lava tree state park, snorkelling at a lava inlet and coral garden and a swim in a natural hot pool. Great fun.
If you stay in Honolulu I suggest, Pearl Harbor and Battle Ship Missouri. Huanama Bay,
beaches on the north shore, Polynesian Cultural Center (requires an entire day and evening).
Have fun, this is a great way to "taste " Hawaii for the first time..