Things you will need;
Tnt-
Redstone torches [detonate]-
Pickaxe-
shovel-
Ladders-
Torches/glowstone
Dirt[I reckon it helps them spawn]
Map
And you seed.
and this website [ Register or Signin to view external links. ]

step 1
Go to the website ( [ Register or Signin to view external links. ] )
Enter your seed at the top --> [ Register or Signin to view external links. ]
and then click Update Map.
It should then look something like this --> [ Register or Signin to view external links. ]
Each green square represents a slime chunk [where the slime spawn 16x16 block]

Step 2
This is where you need you map now, Take out you map at look at the "x" and the "y" co-ordinates. Take you "x" co-ordinates and your "y" co-ordinates and enter them into this box --> [ Register or Signin to view external links. ]
Once done that then click go there. It will centre your slime finder and place you to the nearest co-ordinates with slime chunk.
Now click on one of the green squares and it should look something like the following --> [ Register or Signin to view external links. ]
Then you hover over once of the green slime chunks and find the co-ordinates. On mine I have highlighted the co-ordinates the ones highlighted in the purple box you go to them first untill there the same as the "x" and "y" co-ordinates of the map. Then you dig down on top of the co-ordinates you have done.

Step 3
Once you have made your way down to bed-rock you then go 4 up of the lowest piece of bedrock. Once you have done that you find which way the co-ordinates go, to get to the other set of co-ordinates [Ones in red box] Once you have dug your way round to the other co-ordinates in this case [-32-32] Notice its in the x16 times tables as this is the area it should be dug out by. Once youv marked out the perimeter of the slime chunk its time to mine it all out [16x16 square] Once this is done make sure its 4 heigh. What I then do is on each wall cover it in dirt and on the bottom blocks add torches all the way around.

And that's it your slime farm is good to go..!

Tips
Put the gamemode on hard and you have more chance of slime spawning..And dont forget NEVER
hit the slime with and sword hit it with a Bow and arrows.!

I do hoped this helped some of you ;)
Please leave feedback as this is my First Tut and also let me know if it worked.