Is anyone using horizontal support and resistance lines successfully? If so, how do you come up with your lines? It seems like everyone has different support levels..
Yes, of course, but you need to do extensive studying to understand what actually works, and how what works acts when it actually fails. Forget the books, do your own research. Study all swing highs and lows in all kinds of timeframes, eventually, if you do it for enough years, you will learn about them.
Placing horizontal lines on prior day's high and prior day's low works quite well when you're daytrading. Of course, if a stock has gapped up or down huge, then it's better to place the lines on the daily or weekly chart.
It takes time, after awhile you will know the market and know when it will take off from a support line... Try CL, it works well.