Start with a couple of long, fairly straight tree branches. Try to find one about 8 feet long and another about 6 feet long. Lash them together with some rope to form a cross. (The long one is the vertical piece.)
You can use a couple of thinner branches as supports for the crosspiece. Tie one end of a thin branch to the vertical piece and the other end to the crosspiece. Allow part of the branch to extend beyond the crosspiece; this is where the “hands” will go. Do this on both sides. (You can kind of see how I’ve done it in the photo.)
You can give the scarecrow “hands” by tying a few sticks together with twine and attaching them to the ends of the diagonal support branches. (I don’t know why, but those stick hands take the scary factor to a whole new level — perhaps because it’s creepy to imagine them grabbing you.)
The easiest way to put the scarecrow up is to insert the bottom end into a piece of pipe (about 2-1/2 feet long is sufficient) that you’ve pounded halfway into the ground. I’ve found this works better than trying to dig a hole for the base or supporting the scarecrow with ropes and stakes.
Decorating the scarecrow is the fun part. In the past I’ve tied on torn strips of old sheets. More recently, I bought some cheap black fabric to give it more of a “cape” or “batwings” effect.
Top it off with a pumpkin (larger ones look better) with an appropriately sinister grin applied with thick black magic marker, and you’re done! (Shining a light on the scarecrow at night is kinda creepy too, and it makes an eerie shadow on your house if the light and scarecrow are positioned right.)
So there you go. Have fun! Bwaaa-ha-ha-haaaaa!