If your client is a novice to exercise DO NOT focus on improving BMD for at least the first 3 months. The guidelines for osteoporosis are aggressive and if you do them right off the bat, you might break the bones.
Instead, focus on improving muscle endurance – lighter weights, higher reps. This will also improve BMD to some degree but the main goal here is to improve muscle endurance as well as ligament and tendon strength, foster exercise adherence and get them used to working out regularly.
multi joint exercises are best for osteoporosis. When it comes to improving BMD, know that it may take a year before they may see a significant difference on medical tests. I have met people who reversed their osteoporosis through proper exercise.
ACE has a very good book for special populations and the ACSM does too. The Resources Page on my site has links to those and many other things that can help you
I hope some of this helps
Joe Cannon MS CSCS