Hi Steve, well done for stepping up! So many events wouldn’t exist if it wasn’t for volunteers.
There are probably a million things you can do but this is where I would start: Assuming the fete has taken place before and it’s just you who is new, I’d first ask what has been done before to promote the fete, what has worked and what hasn’t. I would also ask what promotional channels are currently available if any e.g. is there a Facebook page for either the fete or the village. If not you can easily create one with all the essential information and include video/photos from last year’s fete.
If you can create a small poster, get this on any noticeboards you an find around the village and neighbouring towns about six weeks out. Grocery stores, supermarkets, libraries, surgeries, churches, village halls and coffee shops often have community noticeboards and village shops may well be willing to put a poster up for you too. In terms of messaging, get as much of the fete content on any promotional material as soon as possible. These are reasons for people to attend the fete so prioritise those which are usually popular or you know will appeal. In my experience, the cake stall is always busy. Hope that helps. Let us know how you get on & do share any challenges you have along the way with us.