Speaking as a woman who has logged a lot of miles over 20+ years of cycling ...
1) Make sure your bicycle fits you (
if you've done a lot of long distance riding you've probably done this already, but just in case ... ). Go online to find fitting tips:
http://www.cyclemetrics.com/Pages/Fi..._fit_links.htm and if you've got a really good LBS near at hand, have them help you with the fit. Make sure to tell them what kind of cycling you do. Some LBSs think that everyone races and will try to fit you into a racing position, but if that isn't your style of cycling, you have to let them know.
2) Work on your core. Do crunches etc. to build up a strong core. This will help you sit properly on the saddle. You need to be sitting on your sitbones and not on the middle bits, and part of that involves holding your abs in ... which is much easier if you've got a strong core.
3) Sit on the bicycle with good posture. Stand up with your best posture (and you might compare it to good posture diagrams and images you can find if you google it). Now tuck your pelvis under just a little bit, suck your abs in, and lean forward ... that is basically the posture on the bicycle, and will keep you on your sitbones. You can even try this when sitting on a hard chair ... sit up straight, tuck your pelvis under just a little, suck in your abs, and you'll notice the middle bits lift. Now ... it takes a reasonably strong core to keep that up during a ride.
4) Experiment with saddles. Personally, I like the Brooks B-17 men's saddle. I have had three of them so far, and I'm currently in the process of breaking in the third. Although the breaking in process takes a bit of time and patience (and you have to remember that these saddles will never become soft), it has been well worth it. My first Brooks had about 50,000 km on it before it was stolen. I'd still be riding it now otherwise. But even during this break-in process, my sitbones are sore and that's to be expected until the saddle breaks in, but not the middle bit.
A hard saddle like a Brooks allows your sitbones to support your body and if you sit on the saddle as described above, the middle bits either don't come in contact with the saddle at all, or only just barely ... but no pressure.