Cut the runners so you have 2 leaves and some runner on each side, plant it like an upside down T... That way the runners will run along the substrate if done correctly (if you have adequate light yada yada). Wait for new growth.
From personal experience, planting it 1 node at a time is the best for growth. All the clumps I got lazy with and didn't separate just kinda sat there.
Wait for it to take over.
I started with this (kinda hard to see leaves)
Now I have this: (Ignore the massive hack job in the background) This picture is like a week old and it has already grown another layer.
I've also sold 2 football portions and have a 7x12 portion growing emersed from the same glosso I started with.
Close up: (older picture)