On the longest night of the year, you must gather seven different flowers from the fields in the light of the midnight sun.
Once you've broken off the first one, you cannot speak another word.
You must be silent the whole rest of the night, though you are allowed to laugh.
When you go to bed you must place the flowers under your pillow and in a dream you will see your one true love.
Do not worry too much about the "midnight sun". I think this might just be a convenient way to get the kids to go to bed/shut up and I don't ever recall anyone dreaming of anything significant (except when my cousin dreamt of her math teacher and was freaked out 'cos that for sure meant she'd have to marry him.), but it adds a little something to the celebrations, a special kind of magic. There are other spells that come to mind, but this one is very traditional.
Merry Solstice one and all!