If, after having your hair cut in layers, it looks thin, dead, or stringy, for a quick fix start using a thickening shampoo and conditioner, as well as a volumizer. Just spray the volumizer all over damp hair before blowing dry. 

The next time you go in for a trim, ask your hairdresser to snip an inch off the length of your hair, but not to cut the individual layers any shorter. This will create a more solid, less frayed look.