You can dress the plants up by placing the clay pot into a fancy pot, painting the clay pot with colorful designs, or building a "crate" to hold them by using lattice or slat boards

Wash the avocado pit in water thoroughly to clean it
Push 4 toothpicks about 1/3 to 1/2 way up from the rounded end as shown

Place the pit in a jar filled with warm water so the bottom of the pit is in the water, and place in a warm dimly lit place until it sprouts and produces some roots

Place some small pebbles in the bottom of a pot and fill with potting soil

Plant the pit in the soil and place in a sunny spot, water as needed
As the plant grows repot into a larger pot, taking care to not damage the roots

There are many seeds and other plants that can be started or grown in a window sill
Herbs are great for a window sill, Tomatoes & bell peppers can be started indoors and planted outside when danger of frost is past
Lemon & Orange seeds are fun to plant & watch grow. Plant one or two seeds 1/4 to 1 1/2" deep
Cherry, peach, plum, gourds & melons make wonderful plants to grow
Don't forget to put pebbles in the bottom of the pot before adding the soil
Use an inverted glass or mason jar to act as a mini green house until the seeds have been established