According to tradition, a shower should not be thrown by the bride’s immediate relatives, such as her mother, future mother-in-law, or sister, since it may leave an impression that they are asking for gifts. But this is changing and it's perfectly acceptable for a family member to host a shower these days. Quite often the maid of honor or bridesmaids—share the responsibility.
It is common for a bride to have more than one shower; when this happens, the hosts should consult one another about guest lists to avoid duplication (though bridesmaids are typically invited, though not expected, to attend both). Showers are generally held from a couple of months to a couple of weeks before the wedding and shower guests must already be on the wedding guest list.
The invites should go out a month to six weeks in advance. While there are no boundaries when it comes to selecting the stationery-from sweet and simple to high-end, it is recommended to go snail mail only. That said, if a save-the-date seems necessary, an e-mail is still considered completely appropriate. And it is perfectly acceptable for hosts to include registry information in the invitations.