When I first committed myself to exercise on a regular basis I did steady cardio for about half an hour, i.e walking on the treadmill. I then added intensity by increasing speed as well as incline work on the treadmill from 30 minutes to 45 minutes. After about six months I began strength training with FreeMotion equipment doing a full body workout three days a week. I began to enjoy this enough that I then transitioned into free weights and put together an upper body and lower body split that I would rotate every other day. By the end of the year I was doing 45 minutes of cardio and 45 to 50 minutes of lifting five to six days a week. I had great results with this but it took up a lot of time and I always felt rushed.
Currently I am doing about 30 minutes of HIIT, high intensity inverval training during my cardio sessions and still doing the upper and lower split every other day but using mostly compound exercises and super settting. Compound exercises work more than one large muscle group at a time. The super setting is when exercises are done back to back with little rest between each set. For example, I will do 12 reps of squats rest 30 sec and then 12 deadlifts rest 30 sec and back to 12 reps of squats, rest 30 sec and then squat, etc. The compound exercises allows me to work a little more efficiently, no time spent on just doing one exercise per muscle group, and the super setting allows my opposing muscles to get a short rest before the next set begins. It also has the added bonus of keeping my heart rate up.
I have also read the New Rules of Lifting for Women. It does a great job of introducing these concepts to the reader if you are unfamiliar with them. I found a copy at our local library so you may want to check at yours before you commit to purchasing yet another book.
Anyway, I hope this helped to answer your question and enjoy your workouts!