Once you're done with the candle jar, it'll have a little bit of candle left. Put the jar inside your freezer. Let it sit for at least an hour. I had forgotten about mine and left it in for days!
The cold temperature will cause the wax to shrink and loosen from the sides of the jar. Get a dull knife and carefully stab the wax to break it apart.
They come off easily! Trash or save the bits and pieces of candle wax for later use in a candle burner if you like.
Peel off the label. If there is label on the bottom of jar, peel off that, too.
Clean the remaining wax, glue, and soot.
Use a kitchen paper towel so you don't have to worry about leaving sticky stuff on your dish sponge.
Wax can be easily removed with vinegar, baby oil, olive oil, or orange solvent. I find that baby oil works great. It's also cheap.
Rinse out with soapy water and dry with paper towel.
Now you have a jar to reuse and put in anything your heart desires. :-))