You could just window shop the fancier department stores and see what is on the racks and mannequins, making notes or lists of what you like, then go to the second-hand/thrift type stores to see what you could find in similar styles that you like.
I think a nice crisp white blouse and black pants are always classy and stylish! You could change it up with different scarves or pins. You will always look better in things that fit you well rather than trying to disguise figure faults with bagginess.
Do you know how to sew? Even if you don't, again you could look through current pattern books for things that you like and seem practical and then look elsewhere for similar items.