The first thing to do when you pray to Fuu is to try to forget everything bad that happened today. Push all the unhappy thoughts away. If you gave it a try but can't, that's okay; Fuu would understand.
Then you would need to kneel down on that patch of grass in front of the altar. If you're praying away from the shrine, then place a piece of paper, a mousepad, a pillow, anything that serves as a serrogate patch of lush green grass. Pretend that it's a patch of soft grass.
Finally, close your eyes and say your honest to goodness prayer to Fuu. As long as you don't get insulting or anything like that, chances are she'll listen to you. You don't have to clasp your hands together, but you can if it helps.
If you don't have a prayer handy, you can use this one the Groundskeeper recommends:
When you've finished praying, click this.