Mix as much organic matter into it as you can get your hands on: manures, chopped leaves, grass clippings, compost (the best), kitchen peelings, peat moss, etc. The organic matter will help break up the clay and open up the soil so it drains well. If you can find rock phosphate and/or greensand, these are good to add to the beds too. They are slow release, long acting, phosphates and potassium. Water the beds well and let the soil sit and "cook" for a couple of weeks. You'll be amazed at what happens. Then take a soil sample to your county extension agent. They can tell you what you need to add in the way of fertilizer, if anything.

I did this three years ago. During the summer, as one crop finished producing, I would pull it out, add a few bags of composted manure and turn it in again, breakin up the clay more each time. By year two, my soil was in great shape. Now I have a beautiful loose loam. I only have to add nitrogen such as blood meal, cottonseed meal, etc. (I garden organically. If you don't, obviously, you can use synthetic fertilizers.)

Chopped ,partially rotted leave do not have much nitrogen, if at all. Chopped leaves also invite a lot of eartworms.
Actually, organic maters stor away nitrogen at first, the releasing gradually. And that is one of the beauty of them.
Your fertilizer money does not go down the drain, nor your plants would choke on too much nitrogen.

I save all my leaves to mulch with. I am fortunate enough to have an organic compost facility near my house. I can buy certified organic compost or what they call "natural" compost, which was explained as non certified organic. IOW, they don't add anything "unnatural" but the stuff in the lower field, isn't certified.
I pay 25 bucks/yard for certified,and 15 for natural. They also have topsoil at 20/yard,which I use to fill any new beds I build.
For what I cannot produce myself,I use these guys. I always add some, and use some to make compost tea.