Generally speaking, you will either throw the shower for the mum-to-be and make it a girls-only affair, or throw the shower for the expectant couple, inviting the boys along too. However, from experience, we can tell you that most of the men we know glaze over at the typical subjects that tend to come up at a baby shower, from breast-pumps to what colour to paint the nursery.
When writing your list of who to invite, think about who the mother-to-be/couple would like to be there, including close friends, workmates, friends from university, new friends from NCT/ante-natal classes, and of course family members (not forgetting the in-laws!).
You may also want to consider whether anyone has children and whether you want to specifically invite them or not. We usually go by the rule that babies are always welcome, and due to the nature of the event, it’s quite hard to discourage people from bringing their children, but if you haven’t put it on the invitation, they should check with you first. If you really don’t want children there, it’s probably best to throw an evening baby shower.