A little more background information on the space would be helpful for making informed reccomendations. 30 years since it has been cultivated? What has it been since then? What kinds of weeds - is it mostly perennial grasses? What kind of equipment do you have access too? Will you be planting annuals or perennials in the space?
I also have very heavy clay soil, and the biggest problems I have with any newly prepared soil are usually compaction, weeds, and low organic matter. At work we have a tractor drawn rotary plow, but in my own space I'm restricted to hand tools. Here's the strategy I've found that works for me.
I start by tilling the space, removing the plants that are there. I use a hoe for this. To decrease the amount of hard labor I have to do, I'll repeatedly mow the space, prior to tilling, until the perennial grasses root systems have mostly died off. I'll follow this with a tap rooted crop to help alleviate the compaction and improve the soil. I usually use radishes or Chantenay type carrots which handle clay well. Oh, and by the way - if you're farming for profit, carrots and radishes are a lucrative crop - at least here anyway. At work, we sell both at 3$ a bunch, with a good radish bed yielding around 2$ a square foot. Profitable soil improvement!
After I seed, I'll apply a light dusting of
compost for immediate organic matter and soil critters. Radish is a quick crop, so by the time they're out, I'll slap in winter squash to help deal with weeds. They shade the soil and form a dense cover as they mature, so they'll keep a lot of weed seed from germinating. By the next year, the space is more suitable for many kinds of crops. If I skip the first steps and try to plant someting fine rooted first, it usually ends in crop failure.
If I'm planting perennials, I'll do the above steps, but follow the squash with something that produces a lot of carbon rich woody chaff, like grain. After harvesting and knocking the chaff down, there's a mulch for young shrubs that's ready to go - no hauling wood chips around. Planting perennials straight into soil that I haven't run annuals through first usually ends in tragedy.
If I had the equipment, I'd do what Joseph suggests and follow it with the scheme I outlined above.