SAW_LexusIS300

Just went from a 99 Maxima to a 2005 Lexus IS300. Also just went from about 22mpg with Maxima to 17mpg with Lexus (both instances city and highway driving). I didn't expect this and realize that the Lexus IS300 is posted supposed to get approx 18 in city and 23 on highway. Are there any tips/tricks to get better gas mileage? I drive pretty mild most of the time and have added a K&N filter, changed oil, plugs etc. Any input would be appreciated, new to the forum. Thanks, SAW