This is the 668th most frequent Danish word.
smule
A small amount; a little.
Here, "smule" is used to indicate a small quantity of something, in this case, sugar.
Han tog kun en smule sukker i sin kaffe.
He only put a little sugar in his coffee.
"Smule" is used to express a small degree or amount of movement.
Kan du rykke dig en smule til siden, så jeg kan se?
Can you move a little to the side so I can see?
In this case, "smule" indicates a slight degree of a feeling, tiredness.