The bridesmaids luncheon is quite simple. There are no thank you gifts to those important people who have helped her.
Make sure to send invitations well in advance, stating the time and place for the event as well as any directions if needed. Also include the details about what kind of event this will be, whether it will be formal at a fine restaurant or a relaxed picnic in the park. Choose the location wisely, and do consider having this event in a restaurant or other public location rather than at home. Since the luncheon should take place within the week prior to the wedding, or even the day of, it is best to let someone else handle the clean up and cooking. Nonetheless, if the bride feels apt to host at her place, she most certainly may.
Note that the "luncheon" doesn't have to be a luncheon at all. If the bride prefers she can also host a brunch, afternoon tea, or dinner. There's even the option of having a spa party. You can even go to the park, the beach, a museum, a lounge, the movies, or a winery. It all depends on the bride's style and how she wants to thank her special ladies.
As for the date, the bride should take into account whether the luncheon will be followed by any fittings, trips to the salon, or any other last minute wedding detail. If bridesmaids are coming in from out of town, she should consider having the luncheon on the day of the wedding or the day prior to. On the contrary, the bride may opt to give everyone plenty of time to properly primp, preen, and get prepared on the wedding day by throwing this little party during the week before the wedding.