Below I've listed some suggestions as you get started:
Of course, pray. You have been called to this calling at this time with this Primary for a reason. Heavenly Father knows you and He knows your Primary and how you can help them learn the gospel through this wonderful music. You have the inspiration for your Primary. Try not to get too caught up in what others may be doing in their Primary. Do what you think is best for yours. There are lots and lots of ideas out there, and it can be a little overwhelming at first. My advice is to START SIMPLE. What we do is reinforce gospel principles through music. There is no need for elaborate props or schemes. You are your best prop! Be energetic and have fun with the kids. As you become more comfortable and start to figure out what you're doing in this calling, then could be the time to start implementing more ideas and other things you want to do. There is no need to go crazy buying a ton of things, printing a ton of things, working yourself to the breaking point. You will acquire things and ideas as you go. Don't feel like you need to have an extravagant production planned each week to entertain your Primary. Less can be just as good as more (and sometimes better and more powerful). Don't let too many other things get in the way of the Spirit being able to teach. That is the most important thing -- to help the children feel the Spirit as gospel truths are reinforced with them as you sing the songs with them.
Get organized! In whatever way works for you. All of us are different and have different Primary organizations. Do what works for you and your Primary! Organization can look like many things. As one is starting out it could look like having your lesson plan ready for the coming Sunday. It could look like knowing which songs the Primary is going to be singing this coming Sunday and when. It could look like a Monthly Planning Chart. It could look like a simple one page Year's View planning chart. It could look like a Month & Year Planning Chart. It could look like papers in folders in a box. It could look like a list of resources bookmarked on your computer. There are lots of ways you can get organized, but as you start simple and figure out a plan it will make it easier to get your feet on the ground so you can start running. One step at a time!
There are sooo many resources for Primary Music Leaders. You will find endless amounts of blogs and ideas. If you haven't already, read/look through the resources you may or may not know about on LDS.org. And there are many other great resources out there to help you in your calling.
Click here for my list of RESOURCES
Some other helpful ideas:
Posting Song Lyrics
You may want to choose songs to sing that you haven't spent time teaching in Primary, or you're not sure if the children know it. I like to choose songs for Opening and Reverence songs that correspond to the lesson that will be taught in Sharing Time, and I don't always know if they children (or the teachers) know the song. So I've taken Camille's idea of posting song lyrics and tweaked it a bit. I print out the lyrics of these songs and put them up on the board at the front of the room (so I don't have to keep flipping a binder). I know I would have appreciated this as a Primary teacher so I like to encourage their singing by having the words for them to see, and for the Primary children who can read.
...and all those little ones who are wiggly and can't read. They love actions. They need to move. And I've found that predictability works well for them. Have a routine for your Junior Primary. What I've started doing is singing one or two familiar songs with a fun way to sing it (each song we do for this has it's own way) with them at the beginning of Singing Time. I'm slowly introducing a few other good classics this way and also keeping Program songs fresh in their minds. Junior Primary tends to need to learn in smaller portions and with more repetition. And don't get too discouraged if you don't see them singing in Primary. They apparently are learning the songs even though it might not seem that way on Sunday! As you keep reviewing the songs with them they will eventually catch on and they will be ready come Program time. Simple incentives seem to work well for Junior Primary (and Senior for that matter) such as simple games like "Hot and Cold" (where you choose a child to go in the hall while you hide an object and while the child tries to find it the rest of the Primary sings quieter when they are far away from the object and louder as they get closer to it). You might be surprised to find what they actually know!
Holiday themed Singing Time is totally up to you. Don't feel bad if you do them, and don't feel bad if you don't. Maybe you do the ones that are centered on Christ or the Church (Easter, Pioneer Day, Christmas). Maybe you do a touch for all of them, or some of them. Maybe you don't really do any. Don't feel like you have to because it might seem like everyone else is. Just do what works for you and your Primary!
Check back for more!