In general, I prefer to make science lessons hands-on. If you are just looking for a sample lesson, try looking up the standards from your state and seeing what speaks to you. Another idea is to think of a demonstration or lesson you remember. You'll want to choose a stand-alone lesson. Here are some of my favorites:
*Archeological digs with cookies- Get cookies with nuts, chocolate chips and candy, preferably hidden in the cookie. Give students a toothpick and lab sheet. Students first observe the cookie and draw a diagram. Then they excavate it, recording as they go. In the end, they get to eat it!
*Potato chip classification- To teach taxonomy, give students a bag with several different kinds of chips. The chips also need to be made of different things, such as corn, potatoes and vegetables. I like to use plain potato chips, corn tortilla chips, blue tortilla chips, Cheetos, Fritos, and ruffled potato chips. Students then sort and classify the chips by color, what they are made of, taste (spicy and not) and whatever else they can think of.
*Make your own fossils- Gather rocks, shells, sticks, and plastic animals or bugs. Take plaster and have students make fossils to see how fossils leave an impression.
*Jump rope and slinky waves- Use jump ropes and slinkies to demonstrate different types of waves, and have students measure the waves.
*Clay models of the earth- Using clay to build a model of the earth helps reinforce the layers of the earth. Use plastic wrap in different colors to represent different layers of the atmosphere.
Hopefully, these ideas will help get your imagination going!
It really depends on your skill or standard. Science lesson plans that include hands on, inquiry activities are great. For example, I am teaching a unit on rocks right now. I have rocks in my room to show as examples. We are classifying the rocks, identifying unique characteristics, and examining the rocks with magnifying glasses. Giving the students a hands on opportunity will help them remember and apply the knowledge you are giving to them.