The lingonberry might not be the most popular berry eaten raw, which is due to the fact that it has quite a sour taste compared to the sweet bilberry or cloudberry.
BUT, I'll let you into a little secret.;) Wait until the first frost has come or the second or so. In any way they should be dark red when eaten raw. There is another advantage of not picking the first red lingonberries. You don't need to add as much sugar, which gives it a more natural sweetness.
Probably the most popular ways to process the lingonberry here in Lapland is to make jam or juice of it.
Another tipp: Homemade jam with moose meat. Delicious!