Tuck a sachet bag between your guests' linens a day before your friends arrive, in a subtle scent like lime, cucumber, or melon. Or spray L'Occitane's linen water in verbena on the sheets—everybody loves it.
Four pillows are ideal, so your guests can prop themselves up in bed to read or watch television. Lay out slippers, because who remembers to pack slippers? You can buy inexpensive terry cloth ones at Price Club or Costco. They can be a gift for your guests to take home.
Always put a light snack such as fruit and a nice bottle of water by the bed, because a lot of people feel funny about asking for something to eat. Also, put an alarm clock in their room. If your guests have to catch an early plane, they won't have to ask you to get them up.