My personal trainer said to do a full body workout 3 times a week for the first three months using 3 sets of 10-12 reps, after six weeks switch the exercise routine to avoid plateauing. following the first 3 month peroid do 6 weeks of heavy weight 3 sets 5 reps. Is this good advice or should i start isolating the muscle groups? Ive been working out for 1.5 months now