People don't want to walk away from your party feeling inadequate. If you want to increase the odds of being invited to other people's parties, keep yours simple and approachable! That way people won't think, "I could never invite so_and_so to my party, it's not nearly as amazing as hers was and I don't want her to think I'm lame." Trust me guys, it works that way. Sucks, but it's true. Be real, make it fun, keep it simple!
Figure out who's coming. Get that guest list going. Ask the wedding party. Ask the mother of the bride. Ask the person of honor. Ask the couple, if this is a couple's shower. Get a final guest list everyone can live with. And get the addresses, like now. Hunting down addresses for people you don't know is all kinds of not fun, so ask for those with everyone's guest lists right off the bat.