I just let it do its own thing. As long as the leaves are green, they are providing food to be stored for next year's flowers. When they are completely brown they can be removed.
Incidentally, the current thinking is not to tie up daffodil leaves, for the same reason as above.

Agree with Landgirl - I usually cut off the flower stalks, but leave the foliage for a while, unless its bending over everything else, when I may cut it down by half for taller varieties,leaving the rest till its brown. And Daffodil foliage should be left in place as they are, not tied up, and can removed or cut off six weeks after the flowers have finished.