Remember Hawai'i has scores of great beaches on all islands. Some are much less populated than Waikiki, yet offer great views and great waves. Remember you're somewhat closer to the sun in Hawaii than in North America, and the Pacific sun has no mercy. Limit your exposure as much as you can. If you must bake on the sands, be sure to lather on the sunscreen to protect against ultraviolet rays, even if there are clouds in the sky.
Some beaches are more fun and more safe than others.
Be sure to check with lifeguards and local residents for any given length of shore if you have any doubts. Some stretches of sand, like Sandy Beach and Makapu'u Beach on Oahu, are safe only for those experienced in these waters. Again, your lifeguard is well informed on these matters. If you've never tried board surfing before, Waikiki Beach is the place to learn. After all, surfing was invented in Hawaii, and it has been going on at Waikiki for probably several hundred years.