Originally Posted by Draconius

I've always found the diamonds near lava...that's the only way I knew to look :0

Originally Posted by minecraft wiki

There is no evidence that lava pools enhance chances of finding diamond. They merely spawn at about the same altitude. If you see lava, it doesn't necessarily mean there's diamond nearby, it only means you're in the bottom 16 layers of the world, the altitude where diamond also spawns.