Wedding showers are organized especially by a lady who prepares to get married, and rarer by a groom. Nevertheless, there are situations in which a groom also celebrates a shower with his buddies, without organizing a further bachelor party.
Because wedding showers are regular parties, they should be treated as any other party, this meaning that the bride or groom that organizes such event, should start by sending wedding shower invitations. The etiquette says not to send invitations to a shower to a person that was not previously invited to the wedding as well. It would be more than awkward for a person to be invited to a wedding shower, but not to the wedding itself.
Another thing mentioned by the wedding shower etiquette is that a bride could organize more than a single shower before her wedding and not necessarily to receive more gifts (as many could say), but to party while she still can with her girls; after the wedding, it is assumed that she will start playing the role of a married woman, thus she will offer most of her time to her husband, and less to her girlfriends.
An interesting idea related to bridal showers is to play all sorts of games, that will allow your girls to get to know you better, especially those girls related to the groom, not to you, the bride. His sister/s will learn more about their future sister-in-law by participating at such kind of bridal shower, where the bride decides that playing some games is the best idea.
Another idea is to let the girls show their musical talents; for this, the bride has to organize a sort of a karaoke bar, and let the participants sing their lungs out.