I have been lifting for over two years now - trying to work mostly with free weights but some machines too, just not the "isolation" exercises. When I started lifting, I used a book "New Rules of Weightlifting for Women" - it was great as a starter. I was also doing it at home, so no trainer possibility. After half a year my home weights had become too light, so I joined a gym and got the best trainer possible - unconventional ("ass to grass" squats, full range of movements, focused on building muscles and strength in women as well as men etc), strict "no-life-outside" and very knowledgeable. Now two years later I still lift (complex free weights, pretty intense programs which I change once a month). Two months ago I started Crossfit and LOVE it! I am not super strong - still cannot squat my own bodyweight or do more than 3-4 strict chin-ups but I certainly feel that I am stronger than I ever was and going the right direction. And my behind indeed looks pretty good - squats&deadlifts are the key
So from my experience I would advise the following:
1) Do mostly complex free weight exercises (squats, deadlifts, presses, pulls, rows), making sure that your technique is spot on. I would use a good program or book, like the ones mentioned, if a good trainer is not available.
2) Rotate programs once in 4-6 weeks, concentrating on very heavy lifts/low reps(4-7)/longer rest one month, heavy lifts/higher reps (8-12)/shorter breaks the other month.
3) Make sure you rest enough (I like split upper-lower body training because I don't always recover well enough from the more intense programs, but it is not essential)