This is so simple you will wonder why you haven't already been doing it. In a nutshell - shred up all your junk mail along with things like cereal boxes, etc. and then instead of throwing it in the trash, simply rototill it into your garden. (This assumes that you have a garden and a shredder.) It keeps the stuff out of the landfills and turns it into mulch and fertilizer in your garden instead.

Step 1: Background

I used to burn up most of my junk mail and such in my wood stove in the winter. However things like stacks of papers and catalogs don't really burn well, you have to keep stirring them up to separate the pages so they will burn. I also used crumpled newspapers to start fires. The downside was that crumpling them leaves your hands all black from the ink. Eventually I came up with the idea of shredding the stuff and then using it to start fires since it burns way better when cut up. So I saved bags of shredded paper for starting fires in the winter. Problem was that I was shredding way more than I was burning. So several years ago in the spring I decided to try tilling the stuff into the garden. At one time this was a no no because the inks were lead based and there were other not so good things in the paper. But since recycling paper took off, the inks have been cleaned up and many are soy based and so are harmless.
The Results?
The shredded paper just disappears in a short time. The little bit left on the surface even degrades. The paper helps hold moisture in the ground and when it decays it adds nutrients to the soil. It breaks down way faster in your garden than it does in landfills and you get the benefits of the organic matter. In addition I have noticed that my earthworm population has increased a lot. I guess they are working at being educated with all that junk mail. And for those of you who are concerned about things like identity theft, nothing leaves your property, its completely gone, turned into compost.

Step 2: You Need a Good Shredder

My first shredder was a little cheap one. It didn't last long. The next one was a cross cut shredder. These are much better if you're tilling in the paper since the long paper strips from the strip shredders tend to wrap around the tiller tines. After that one wore out I finally got a heavy duty model. Save yourself some money and buy the heavy duty one first. It can shred more at a time and does a better job. Also I discovered that it has no problems shredding cardboard from boxes like the ones from frozen dinners and cereal. The cardboard is actually even better for the garden. It tills deeper and what is on the surface doesn't blow around. I pack all the shredded stuff in plastic bags and store it until spring. Make sure to be careful where you store it because it if it gets a spark it will burn really good so treat it like a combustible.
My current shredder has a 15 sheet capacity and cross cuts to about 1 1/2 inches.

Step 3: Spread and Till

Its a very simple process. Spread shredded paper around by the handfuls until the ground is all covered and then till it as deep as your tiller can go. The dirt will take care of the rest. I have an older Troy Built Horse tiller but I also have a large garden plot. You can get by with a smaller tiller and a small plot, the important thing is to get the paper mixed with the dirt.
For one individual this is really just a small thing, a bit of paper put in the garden instead of the landfill. But if a lot of people start doing it, it can make a cumulative difference. Imagine how much tonnage will be spared from landfills and instead put back to work growing vegetables if all the gardeners in the country started doing this.

Step 4: Bonus

I have been gardening for a long time and there are a few little things I picked up over the years.
One of the better ones is that I plant everything in furrows and then rather than sprinkle with a sprinkler I flood the furrows. This saves water since you're watering the plants only and not the bare ground. It also helps with weeds since the weeds won't germinate if the seeds don't get water. And the garden plants get a deep watering since the water doesn't run off. This will not work so well if you get a lot of rain, in fact it might tend to drown your plants. But in the arid west it works really well.

Step 5: Bubbler

A problem with flood watering is that the high water pressure can actually dig up the plants. Yet another piece of junk came to the rescue. I took an old sand filter from a well that was kicking around and various pipe fittings and adapted it to fit the end of a hose. The brass sand filter was originally designed to keep dirt from getting sucked up by the wells pump. It has a bunch of little slits in it. It turns out it also works perfect for reducing the water pressure so it just bubbles out and flows calmly down the trench. It's also big enough that it's hard to lose or run over with the mower. Important if you have kids helping with the garden since those types of things seem to happen a lot.
You can make your own version of this by using PVC pipe. Cut slits in a short piece of 1 1/2 or 2 inch PVC pipe, 6 to 12 inches in length. You can use anything to cut these, a hack saw, a Dremmel , most anything that can cut a narrow slice. Glue on an end cap and fittings to reduce it to the size of a hose adapter. If you cut enough slits the water should just flow out and not dig holes in the dirt.