Hi Jasperina, I began lifting with a trainer, and was with him for most of my first year. He made me start with teensy Barbie weights, which was really smart. I learned good technique, built muscle endurance, and didn't get hurt. After that year, I had developed a strong core, knew how to use it when lifting, and had reasonable form. I lift on alternate days, and do core work and walk, or row, or use an elliptical on the days I don't lift. I'm small, 5'3.5" and 102 pounds, 28-29% bodyfat according to my DEXAfit scans. I lift what feels heavy to me. I try to be sure to work all muscle groups every week. I use weights that I can get 10 reps with, and then in a second or third set, I increase the weight by a small increment, and work to failure, whatever that might be. Sometimes just one or two reps feels like a victory, but if it seems TOO heavy, I wisely give up. I love Planet Fitness because of the machines that allow a 2.5lb weight increase, which works for my tiny frame. In my first year, I got to bench pressing two 15# dumbbells and could not make the transition to 20#, until I went out and bought a set of 17.5#ers. Now I know lots of tricks like adding washers to my barbell, or adding 1# wrist wrap weights to my bar. When I seem to have reached a stopping point at adding weight, I go back to a substantially lighter weight and do sets of 15 or even 20 reps for a while, and then gradually build again. I have recently added a vibration plate, and will be curious to see how that works out for me. Wishing you luck and progress in your bone building journey!