Is it going to be a lunch or a dinner? Adults or children? Adventurous eaters or prefer bland/beige food, or a mix? Any dietary requirements, allergies, vegans/veggies or fussy eaters to cater for? Budget roughly? And also (related to budget) are you averse to buying in ready made, and do you want there to be hot items as well as cold? A 'finger' buffet or will there be seating so people can eat with forks?
For a classic, very safe, likely to appeal to most English lunch buffet I would do:
-Big cheeseboard with grapes, chutneys and crackers
-Plates of cold meats (ham, salami etc)
-Smoked salmon (possibly served on ready-bought blinis or melba toasts with cream cheese and chives, if being fancy, or just on platters with lemon wedges if not)
-A big green dressed salad
-A big tomato based/greek salad
-A big pasta salad (assuming possible to eat with knives and forks)
-Lots of fresh crusty bread/rolls (so people can make up sandwiches if they wish or just eat on the side)
-Quiches, tarts, sausage rolls or pies bought ready made (can be warmed in oven or just served cool)
-Bowls of crisps and nuts
-Vegetable crudites and dips, breadsticks
-Some trays of ready bought 'party' type oven food usually from M&S - mini sausage rolls, cheesy bites, breaded prawns, that kind of thing (adjust fanciness according to your desire).
-For pudding, a large pavlova or Eton Mess (ready made meringues unless you particularly want to make your own) with lots of whipped cream and fresh berries or tropical fruits - and/or scones with fresh cream and jam and/or ask other guests to bring along a dessert
But I have also successfully done 'hot' buffets before (which I would think of more for an evening do) or more Mediterranean 'mezze' style spreads which are particularly good if you have veggies or vegans coming but may be less suitable for fussy eaters, so can post ideas for these too?