I have taken over an allotment at this time of year previously, and would suggest taking time to clear the site of any weeds and debris and digging it over so that next spring it is all ready to go.
Allotment Boy said:
If you want to grow fruit then you could plant that now, if you have clear space but otherwise I agree clear, and plan now. Cover any areas you clear, so weeds don't regrow. Take it easy though, over many years I have seen too many prospective plotholders, come all guns ablaze, then get put off and give up again. Do a bit at a time slow and steady wins the race.
I think I see some rhubarb, near the back, towards the right in the picture. That might be worth keeping if you like it.