You remember as a kid folding paper and cutting snips out of the paper to create a snowflake. Try making paper snowflakes in varying sizes, placing the larger ones around the bottom third of your tree. The mid-size paper snowflakes on the center and smaller snowflakes around the top of the tree will make your tree look like it is covered in homemade snow. For color, use construction paper to create your snowflakes. Here is a link to a video on how to create a paper snowflake from a square piece of paper. And this website tells you how to create a snowflake from a circle-cut piece of paper.
Using dried flowers takes some advance planning. I have a large hydrangeas shrub from which I collect blooms each year for drying to use at Christmas time. That is the nice part about using dried flowers to decorate a Christmas tree—you can throw the flowers out after Christmas. Check out this article, BestFlowers to Grow to Create Dried Flower Wreaths, for ideas on other flowers suitable for drying to use as part of your Christmas decorating theme.
Collect pictures of Christmas scenes or kids at Christmas over the years. Snip pictures in different shapes like oval, rectangle, square, or diamond. Consider keeping the shapes about 6 inches across or smaller. Glue the picture to a same-shape piece of construction paper that is slightly larger to create a border around the picture. To attach the picture to your Christmas tree, poke a hole in the top of the paper frame to run a ribbon, string, or wire tie such as those used to close a bread bag.
This is my favorite homemade decoration—Christmas cards. Cut off the front of your favorite Christmas cards. Christmas cards are sturdy and will not need a construction paper backing. Use red, green, or white ribbon for a classic look to hang the Christmas card on your tree.