Thanks for writing. I'd add as much organic matter, such as compost, to the soil as you can --- this will help break up the clay so your vegetables can thrive. You can also mix in some well-rotted manure if you like to additional organic matter and nutrients.
Here are more tips for starting a vegetable garden from scratch: http://www.bhg.com/gardening/vegetable/vegetables/planning-your-first-vegetable-garden/
Now as far as planting goes, your average first frost date is October 30 --- so start with that date. Look at the average number of days it takes a variety to mature (you can find it on the seed packet) and count backward from the October 30 date --- that will tell you when you should plant your varieties to get a fall crop.
For more information, check out http://www.bhg.com/gardening/vegetable/vegetables/"