Congratulations, how exciting!
I've had an allotment for 5 years now and it's great exercise and for growing veg but it is very time consuming. What I would suggest is to read the contract very carefully, there isn't a standard one some have all sorts of rules and regs, others are much easier.
Check where the water is if it's available, hopefully there will be a tap nearby, ours is serviced by old livestock troughs rather than a tap. I have a standing waterbutt to collect rain but it's never enough in the dry periods. Check to see if there is a natural area for composting, if there isn't it's worth putting one in. Also check what shed sizes you are allowed and never keep anything in it that you can't afford to lose!
Check the site situation, shade, sun, go up at different times of day if you have to. Mine is in a lot of shade but if I go up first thing it's bathed in sunshine for around 4 hours which is handy to know. Check the soil, pH is useful but not the be all and end all, soil structure is important, knowing if there is an area that could be improved for drainage or is very dry so you can site appropriate planting.
Many allotments allow raised beds but check your contract, we do no dig and the beds have no raised element except when I start out with the wool cardboard, compost layering this time of year ready for planting out in spring. I took a note book with me and a measuring tape so I could plot the beds straight away and then the sun/microclimate/soilstructure to inform planting plans, perennial veg and fruit, rotation of annual veg and fruit.
Check for any existing structures ours had broken down outbuildings that were dangerous, we asked the council to clear these off which they did do. Sometimes though you can be lucky enough to inherit a shed, greenhouse, or fruitcage.
If you can meet up and chat to the other allotment holders, they can tell you lots about what does well on the site and some can be really helpful to new allotment holders, although a few can be a PITN too.
Oh and something I didn;t pick up for a while. If for any reason you can't get down there for a coupld of weeks let the manager know why and for how long, it saves them sending letters about the state of your allotment if the weeds have got in while you are caring for someone or have gone on your hols.
Best of luck I hope you enjoy it.