Go to settings > General
Tap on Accessibility
Then under Hearing, turn on Custom Vibrations then go back...
Tap on Sounds
Go all the way down to Vibration Patterns and tap it
At the bottom , tap on 'Create new vibration'
Simply tap to create your pattern and stop when finished
just play around until you find one that you like then tap save
Add a name to your pattern
and it's set! now go to one of your contacts...
Tap on Vibration
Choose your custom pattern and tap to set it!
If you have any questions, just comment and i'll try and answer them asap