Always try to use the potatoes with out leaving longer. Potatoes always go dark soon. Then the colours will not be nice.
Squeezing the extra liquid is not that easy. But do as much as you can, or dry on a paper towel.
When you wash the green part of the leek make sure to seperate the leaves first and then wash one by one to remove the mud or dust on it. leeks easily collect mud.
I always like extra taste. You can always reduce or omit stock cubes. I used the vegetable stock cubes.