If you have no keyboard at all, do as shown above. If you have the old keyboard but not the new iOS 8.3 keyboard, make sure your doing it right. Many of the emoji don't have the new skin tone options. These do in the screenshot. If these don't work, try a hard reset. Hold the top power/sleep button and the home button at the same time until the Apple logo appears, then release.
Sent from my ancient but trustworthy iPhone 5. ☮