In DragonVale for the iPhone and iPad, in order to add friends you have to add or accept them in the Gamecenter app on your phone.
To add someone to Gamecenter, you need to know their Gamecenter ID. Everyone that plays has a unique ID that identifies them. If you know someone’s ID, simply click the + in the top right corner and add it.
To accept requests, open the Friend Requests section in the Gamecenter app and accept any requests sent to you.
Look down in the comments below for people leaving their GameCenter ID for adding friends. Leave your ID there as well to have people add you!
Also check out my How to Get Free Gems guide, several people have posted their Gamecenter ID’s there as well.