I am also studying elementary education and have the same feelings as you! It is very nerve wracking! I think the best way when they are doing their first experiment is to show them as an entire class the way it is supposed to be done, so that they all have the same experience. This way when they do it by themselves, they know what the end result should be. Also, especially with the younger children, I think it is important to ease them into it. Start really simple and build up from there. Once you get to know your students, I am sure you will know what is best for them.