My biggest tip for plots that need work is to invest in weed fabric, the proper stuff, that lasts years and years and try and level your plot as much as you can and cover half or 3/4 of it whilst you work on the first 1/4. Do that really well and if you have to, where the sides of the weed fabric meet, open them up a little and plant some squashes to grow over the covered area in the first year so that you can show you are using the whole plot [and so you don't get kicked off], and then fold it back as and when you have the first 1/4 under control.
Allotments are hard, hard work. We worked mine, religiously every day during the spring, summer and autumn and every week in the winter for a decade. It had been stripped of all the top soil and even after 10 years of adding organic matter was still rock hard in the summer and slippy mud in the winter.
We one year added manure which turned out to have aminopyralid and it never properly recovered. I tried the Back to Eden method using heavy wood chips but all that did was create more nutrients for the perennial weeds to flourish. We tried almost everything over the years but still got very little crops to actually properly grow.
So after a decade of doing this, we nearly gave up. But I decided to put my 'school gardening' hat on and said to myself 'what would I do with this plot if I was doing this in a school?'
So I raked the whole lot as flat as a pancake, bought weed fabric and covered it all. Then bought 27 pallet collars, and 6 tonnes of topsoil and made raised beds all neatly over the whole thing. And I had more harvests that first year than I'd had in years. It cost me around £500 in fabric, pallet collars and topsoil but we got more than that back in the food we could grow. I cropped year round for 3 full years, the beds were never empty, it was easy to use blue pipe and netting to cover what needed covering, things could be grown so much closer together it was a complete shock as to how much I got out of it.
So my advice is to cover what you can't tackle and whilst you tackle a smaller piece, just bung some squashes in the covered bits so that you don't get kicked off. If you can't afford weed fabric, then cover it with flattened cardboard and weigh it down.