Have fun! It is very overwhelming to run a practice if you are not prepared. Treat the players like they know nothing about the game and start everything from scratch. By doing this it will force you to teach them the game and that way you will all be on the same page.

Always have a plan. You must go to every practice with a well thought-out plan. The players will know right away if you are just trying to wing it. They want structure, and if you can show them that you prepared yourself for the practice, they will know that there is structure. Explain to them what they will be covering and you will see that the practice will go much smoother.