I started really close and worked my way back. I rarely miss anything outside of 20 feet anymore. I put with a completely different stance outside of 30 feet, so it had no real affect of my long putting. The repetition and the dedication is what really makes the difference.
It worked for me. I started at 15' and I constantly practice at that number on up to30' or so. I found my long putting improved, because I found I didn't need to jump putt until approx 40' out. All said, putting has always been my priority. Since I don't throw for much distance. So I do spend quite a bit of time putting in my spare time.Some of the new players at our course call me "The putting guy" Since that's all they see me doing.