This is what we found worked best:
In a big bowl:
2 cups Elmers glue
2 cups of water
Couple drops of food colouring or water colour
In a smaller bowl:
1/2 cup Borax
2 cups boiling water
Stir slowly, letting all the Borax dissolve. This is a good way to practice patience.
Once Borax is dissolved pour into the big bowl.
Slowly stir and it will start to clump together.
You may need to use your hands to finish mixing the water with the glue. Careful as the water can still be hot.
Once most of the water is mixed with the glue- It is done.
Once done it is fun to make "Flubber bubbles" or put in a strainer and let it ooze out of the holes and cute with scissors. This is endless fun!