There are many great biology fair ideas out there which can give you an interesting hands-on experience. You just has to decide where your personal interest lies and go from there. The choices are considerable and can be involve using animal, plant or even human project ideas.
First you must formulate a question based on a topic which interests you; in other words pick something that you always wondered about or were intrigued by. Once you have decided on the topic question you wish to explore, you can then go about answering the question through the use of the scientific method.
The scientific method, which involves choosing that question also involves stating the hypothesis you wish to find true. Once you have done this you can gather your materials and perform various experiments to see if your hypothesis is true or not. So gather your data, but remember to only use one variable in your experiment, as well as one control.
If you are thinking of doing a biology fair project on an animal, you can do your research on animal life, behavior or anatomy. While you can't necessarily experiment on the animal itself, there are many models around you can use to gather your information.However, if you want to use the real thing, there are many ideas out there that are not harmful to animals. For example, you could study how fish behave when exposed to music, or do lights attract flies or ants? If you have a cat, you can study how your cat behaves when it hears birds singing. If you have the time to study your pet more in depth, you can study its eating and drinking behavior to see if it eats or drinks at certain times, or how often. If you have a pet bird, a simple but fun experiement would be to test what birdseed your bird prefers. These are just a few ideas for animal studies.
If you wish to study plant behavior, a good study would be to see if different color lights make a difference in which direction a plant grows. Another idea you could try would be to check the pH of the soil where a plant is growing to see if different pH's have different effects. If someone in your family smokes you could test the effect of smoke on a growing plant. It could also be fun to see if music affects plant growth, or even if different types of music show a difference.
If your choice is a human subject, you could test the five senses to see which sense best helps you identify a food, when you are not looking at it. You could also keep track of your/someone's mood when the weather changes and even do some research into what type of exercise helps build muscles the best. If you can find people willing to participate in your experiment, you can even test to see if different people have different "normal" body temperature. You may even be able to get some people to let you take their fingerprints so you can compare them. Or how about looking at different types of hair samples under the microscope, or how eating breakfast affects a students performance at school?
These are just a few ideas for a biology fair. There are so many possibilities out there; you are bound to find something to interest you. Try and find something different that will interest others too. You want to make your project as interesting and as fun as possible.