Just a few ideas - from when I took over a badly overgrown couple of plots.
- work out where you want beds; it's a lot easier having beds about 4 foot wide and whatever length you want.
- clear the beds, one at a time; it took three years to get my "bad" plot all into cultivation. If necessary, cut the rough stuff back. And cover whatever you've not cleared with thick black plastic sheeting or some equivalent to starve the weeds of light.
You have a few choices to make
Organic? - my choice was to dig by hand - and remove all the grass and roots to what I grandly called my compost heap (but . . . it worked!). Don't put bindweed, ground elder, marestail in the compost heap, but anything else goes! Caveat - I enjoy digging.
- rotovate - hire/borrow a rotovator; personally, I wouldn't choose this, as it chops up all the roots of the nasties, - and from each chopped bit of nasty root, another nasty grows soon --------- unless you have the permanent use of a rotovator; in which case, it's a trial of patience. Who outlasts the other? In time the weeds will give up trying!
Not organic? - use roundup or similar weedkiller; follow the instructions on the pack; my only venture using this was not a success, but loads of people swear by it.
But the real key, I am sure, is to get a small bit really well-cleaned and ready, before you move on to the next bit!