I recommend that you head over to the Soil, Compost & Mulch forum here at Gardenweb to repost your question - it's a much more active forum than this.

I wrote this for someone else who asked a similar question, hope it helps you get a handle on how you think you should get started, depending on your circumstances... sorry if some of it doesn't apply, I didn't read it through again just now.

If you've got more time than energy, like I do, smothering and lasagna is the easiest way to start a new garden bed for free, or almost. Sooo much easier than digging up grass. Just spread newspaper (about 10 sheets thick) or cardboard, overlapping well, until the area you want to be a bed is covered. Then cover the paper with 4-6" of finely shredded mulch and wait for the grass to die, usually 4-6 weeks but could be longer for some grasses. I've done this many, many times.

My latest one is really ugly but I'm just trying to make lemonade out of lemons with this one... drought (probably aided by grubs) killed the grass here so I decided that would be the new sunny front bed I was considering. I did dig out a little spot that had hardly any grass and put some Cannas and Gladiolus there, a tiny baby maple tree, some Hibiscus cuttings which still just look stupid 'cuz they're "dead" sticks in the ground, then kind of working around it with smothering, and bark chips, which aren't my preference but I had them available. They don't stay in place if it ever rains really hard. Anyway, with this, I'm not planning to leave the bark chips there, they're just making sure the newspaper is held firmly to the contours of the ground to block the air and light from reaching the grass, which is what is needed to kill it. Whenever I can find more shredded hardwood, I'll replace the bark chips.

Anyway, the newspaper decomposes and does not need to be removed later, just dig through it to add plants in the ground.

I've also smothered grass with stuff that was handy, but does have to be removed to use the bed, like sheets of metal, old egg crate mattress topper, the bags of mulch that will cover the spot, whatever's handy. I think it's easier to wait for the grass to die than dig it up, and I don't mind if it has to get more ugly in the process of getting more pretty.

One other benefit of smothering with a leave-in-place substance like paper or cardboard is that the weed seeds that may be in the ground are unable to germinate as they might be if you just dug up the grass and/or tilled.

The lasagna comes into play if you add amendment layers to your smothering. For example, you could put the paper/cardboard, then kitchen scraps, ready to use compost, leaves, yard trimmings, whatever organic material (OM) that is handy, then the mulch (or not, if the other stuff is a thick enough layer to hold the paper in place and block the light.) It's not necessary to have lasagna layers when smothering, but when planting later, there's a huge improvement if a lot of
OM was placed there.

AND, while you're waiting, you can set potted plants there...

I wrote this for someone complaining about clay, which you...

September is actually a perfect time to plant trees, shrubs and bulbs. They are less likely to be burned by the summer sun and drought, and the cool air encourages to focus their growth on roots. Many garden stores have sales around then, because despite all of the above, people stop thinking of gardening.

Avoid chopping down anything or pulling anything out the first year. A lot of people chop down things that turn out to be rare bloom ornamentals or fruit trees.

Also a good time to start a compost heap. It will smell less and you can fill it with Fall leaves.

It might sound simplistic, but have a plan. Spend some time with organization so that you know all the whats and wheres before you get too involved and try to make snap decision.

Locating quality plants in September or October might be a bit much, so spend some time now going around to the various vendors to inquire what they intend to have available.

You should be able to do bulbs this autumn and you might be able to locate some other things. My experience has been that spring planting of fruit trees yields better results.

There is a lot to be said in a favorable way about planting in after Labor Day, a lot depends on what you intend to do and where you want to plant it.

I will mention something that always sticks in my mind. Observe first, plan second, plant third. There might be some spots in your yard that snow will not cover or might be there all winter and that can make a difference with whatever you plant there.

Jim