Trims!!!
A key to maintaining long hair is getting frequent trims. Do not assume that because your hair is long, you can simply let it grow. By continuing to get it trimmed regularly, you are keeping it shaped and reducing split ends, thus making your hair healthy.
Just a 1/4 to 1/2 inch every 4 to 6 weeks will make a big difference in getting split ends. Also using a high quality reconditioner frequently will keep your hair from getting frizzy.
Long hair is beautiful, but does take some work to keep in looking great.