The best way to force twigs is to cut one to two foot long branches from a flowering shrub or tree, bring them indoors, and place them in water. A vase or even a can or bucket can be used to hold the branches and water. Good plants to try include forsythia, any of the dogwoods, pussy willows, apple, cherry and flowering almond. Talk to an adult about which plants in your yard or neighborhood are usually the first to leaf out or flower. These will be the ones that will respond quickest to forcing.
Many trees have interesting flowers which most people overlook.
Try forcing maple , oaks, willows, ashes, Horse Chestnut twigs, or any other tree you can get a couple of fresh cut branches from. Click here for a diagram of a flower with parts labeled. Tree flowers are not always so spectacular. Use a hand lens or magnifying glass to look for different flower parts, sepals, petals, stamens, pistils. If the flowers have stamens but no pistils, they are male.