Use this method with roses or any other flower--they last for years if you take care of them right!
You'll want to wait until your flowers *just* start to die. Enjoy them while they're alive until they start looking a little sad.
Step 1: Supplies
You'll need string, scissors and your flowers. You'll also need a place to hang them.
Step 2: Get Rid of the Ugly Parts
Pull off any petals that are already coming off, and trim off the leaves if you don't want them. (I prefer to take all the leaves off)
You'll notice that at this point the rose is basically at a 90 degree angle to the stem. Hanging it upside down will fix that right up.
Step 3: Cut Your String
Cut your string into as many lengths as you have flowers to hang. I cut them around 10 inches or so.
Step 4: Tie String to Flowers
Tie your string to the flower. Try to find a nub to tie it under so when you hang it upside down the string won't slip off.
Step 5: Hang
Tie all the ends of your flowers' strings to something. I happen to have an empty curtain rod to hang mine from. You can also try tying a couple to several coat hangers, and then you can hang them anywhere. When I was a teenager I would thumbtack them to my ceiling (it looked awesome!). Pro Tip: tie a double knot.
It's very important that wherever you're hanging them is relatively dry. Don't hang these in your bathroom to dry out. Once they are dry, they will still need to stay somewhere kind of dry, so nowhere too humid.
Step 6: Ta Da!
Wait a couple weeks and you have some lovely dried flowers to decorate with.