practice certainly does make perfect, but you might want to try surrounding yourself with new lyricists as much as possible. people who have really helped me develop my lyric writing in the past are Conor Oberst of Bright Eyes (specifically his later BE albums and solo work - super personal, very deep spiritual and cynical undertones and some intense and beautiful imagery) and Kevin Barnes from of Montreal (if you can get through your first listen, take a look at 'The Past Is A Grotesque Animal' - it's a confessional titan of a song). obviously the greats like Paul Simon, Bob Dylan etc. are fair game as well.
try reading a shit tonne of poetry. i tore up plath, larkin, eliot, ginsberg etc. for a year or two in school and i certainly noticed some improvement.
most important of all of course is don't try too hard.
