Plan what she wants.
If the bride doesn't want to hit the strip clubs or fly to Vegas for a crazy weekend, don't pressure her. If what she truly wants is a quiet evening in with all of her favorite people, plan something cozy, fun, and low-key. Even though some women love the humor of more stereotypical bachelorette fare (such as NSFW decorations and favors), others prefer to use this as a time to unwind from wedding planning stress and focus on their girlfriends.
No matter whether the bride wants to go wild or not, bachelorette party planning also involves practical considerations. First, everyone needs to be able to afford it. Often party guests cover their own costs and then chip in for the bride's share (the hostess can also pay for the bride). As the hostess, be aware of how expensive this type of event can be and try to plan accordingly. As a side note, don't worry about giving the bride a gift--they are not traditionally given at bachelorette parties (unless time has been limited and the bachelorette party and bridal shower are actually the same event).
Also, consider the schedule you're working with when you plan the bachelorette party. If the only time everyone can get together is two nights before the wedding, an insane night of drinking and dancing is probably not the safest bet. It's better to schedule more lively bachelorette parties at least a week in advance of the wedding, if that's feasible with the guest list.
The best part about bachelorette party planning? You can have so much fun with it. This event is not like a bridal shower or bridesmaid luncheon. It doesn't have to be elegant or serious or impressive. It can be playful and engaging and even really, really silly. You can turn the whole night into something reminiscent of a junior high slumber party, if that's what would make the bride giggle with delight. Celebrate and enjoy!