Diamonds aren't exactly the easiest ore to find usually but with this seed you can get some within 5 minutes!
Dig straight down at spawn. Soon enough you should fall into a cave. Ignore that and just continue digging down.
[gallery link="file" columns="2" size="medium" ids="8478,8479,8480,8481"]
Soon enough you should fall into a second cave which is bigger than the first one but ignore that and continue at the same place just digging down.
[gallery link="file" columns="2" size="medium" ids="8482,8483"]
When you reach the third cave walk down where there is like a big open area with some lava further away. Anyways, here's some gold which you can mine.
[gallery link="file" columns="2" size="medium" ids="8484,8485"]
Continue past the gold and toward where there is water flowing into a pool of lava further away.
To your left (image below) there are the diamonds. Before going ahead and mine them you probably want to block off the water source which pushes you toward the lava.
A total of 5 diamond ores you'll find here but there might be more for you to find if you look around a bit too.