Thick hair can sometimes cause problems as a build-up of hair density and weight can happen in between hair cuts. Thick hair needs to be managed every 6-8 weeks by having the weight taken out by your stylist. Weight is the key as opposed to length, so maintain your style with a reputable stylist that is confident in thinning your hair out.
To keep your hair looking smooth and shiny, apply gloss enhancing products such as Kerastase Oleo Relax Serum to towel dried hair. Then, whilst styling with your dryer use a medium speed, as if you go too fast it will aggravate the hair cuticle causing it to swell up and make the hair look even thicker.
Using a ceramic straightener such as the GHD Mk IV with a heat protection oil can assist the hair fibre to lay flat and achieve a smooth finish and result in a more finer hair appearance.