When you read that 75% of the Earth's surface is covered by water, what does it really mean? The answer goes far beyond just a simple fact. As with many topics in science, the deeper you go, the more you find.
Think of all the colors you can see? Think about rainbows, field full of flowers, and holiday decorations. With all of the colors that we can see, there are many more that we can't see, at least with just our eyes. With the help of a cell phone, you can see some of those invisible colors.
In the scientific process, we should not rely on the results of a single test. Instead, we should perform the test over and over. Why? If it works once, shouldn't it work the same way every time? Yes, it should, so if we repeat the experiment and get a different result, then we know that there is something about the test that we are not considering.
Now we need to design our project so that it will be scientific. This means looking very closely at variables, things that could change the results we get. We want the variable we are testing to change, but we want everything else to be as close to the same as possible.
The very first step in doing a science fair project is to set your goal. Do you want to win the science fair, or just get the project done because you have to? Once that is done, then you need to carefully select a topic for your project. Doing these things correctly will make your project MUCH easier, and the video below will show you how to do that.
What if someone else has already done the project you want to do? Replicating a project that someone else has done is a very important part of the scientific process, but if you REALLY need a unique project, take a look at Thoughts on a Science Fair Project, part 2.
Once you know what you would like to do, then you need to form a hypothesis.