I gave her bits of advice some I had been given when I was given that calling and felt overwhelmed and some I have learned along the way. Since its been a while I thought it might be a good idea to post a few of those (some being posted again).
1- the first advice my mom gave me was that the children don't care how well you sing. I can't carry a tune in a bucket unless the piano is playing the melody. Even with the piano my voice is nothing to rave about. The children don't care. They do care about how loud you sing. They will match you and how loud you sing.
2- You need to have energy. Even if you don't feel "happy to be there" you need to act like you're "happy to be up there" and "be singing". Be positive.
3- Learn the songs, Learn to love the songs.
4- Use bight colors
5- Be simple. You don't need fancy, or completed, or elaborate visuals. Keep them simple.
6- If you have the attention of the younger children-You're doing GREAT. The youngest children in JR primary may or may not sing. However if you have their attention then that is all you need at that moment.
7- What may work for JR primary may or may not work for SR primary (and vice versa). An example of this is JR primary has few children that can read, using visuals with words won't work as well as with SR primary where you'll have more children that can read. Another example is, JR primary (at least in our ward) can easily stay reverent while "doing as I'm doing" while practicing a song (patting knees, swimming, hula hooping). In contrast, SR primary would get silly and rarely be reverent while having actions to do while singing. You would think it would be the other way around, but that was the way it was.
8- Get the teachers involved. I realized that especially during JR primary, the children sang better when their teachers were singing. Also its hard to watch all the children at once, get the teachers to help you by pointing out children that were trying to sing and be reverent.
I hope these are useful and help those of you with anxiety about a new calling to just relax breath and find what works best for you and your ward's children. Good Luck. Heavenly Father called you for a reason. Make the most of it and enjoy the time you have (it will be over before you realize it and then you'll be sad).