Tip #1: Create a schedule but go with the flow...
That is a hypocritical statement but I mean to reinforce the notion that you need to have some balance. You are your kids will need this. The children you are with should understand a rough outline of what their days look like. But you need to put in some spontaneity in the day too. I am a planner so I usually know what I will be doing with the girls I am with on a day to day basis. I may know earlier in the week that on Thursday I am taking them mini golfing but they don't need to know that. I can pull out a little magic and surprise them. On the flip side, I also declare no tv/electronic chunks of a day or a whole day on a whim. Children these days have a lot at their disposal, iphone, ipods, ipads (...thanks Mac). So it is important to remind them and introduce them to new experiences.
Tip #2: Have socks handy
We are out and about during the day and it's summer and most of us are in sandals and flip-flops. I made sure to sneak a pair of each girl's socks in my purse. That way if we are out and decide to go bowling, trampoline parks, or other indoor shoe required/rental places, we are prepared.
Tip #3: Car distractions
This is especially important if you have more than one sibling in the car with you at once. Having things in the car for the little ones to do will help minimize children trying to annoy each other. You don't want to be driving and have to stop a slap fight...trust me, it will happen. You don't have to have markers and play-dough in your car. Something as simple and wonderful as some books can usually do the trick.
Tip #4: Join the local library
If the family you are working for doesn't have a library card, get one. The library has so many programs through out the summer and it is a great place to go weekly, especially on a rainy day. I have found many children's books on tape for them to listen too while following a long in the book. One of the girls I watch absolutely loves the books on tape for the books that are above her reading level yet she still enjoys the stories.
Tip #5: Take pictures
I have done this for every family I have worked for and I think it is really special. I take a lot of pictures through out the summer and at the end I create a scrapbook for the children which documents their summer. I have made it myself and electronically through SnapFish. This year my girls are old enough that we can make one together. It is something I have found the parents really appreciate. They do not get to see everything and every moment while they are at work and I know a lot of parents feel guilty that they cannot be there. This book is a reminder that their children were well taken care of and they had loads of fun a long the way.