blocks: http://www.minecraftwiki.net/wiki/Diamond_(Block)
gem: http://www.minecraftwiki.net/wiki/Diamond_(Gem)
and ore: http://www.minecraftwiki.net/wiki/Diamond_(Ore)
The higher level you are, meaning your level ranking (not elevatiom), the more often diamonds will spawn around you. So, Rank up in levels and then go searching for diamonds. But make sure not to die and lose your levels.