I don't have a good suggestion. As I said I work backwards by looking at market P/Es to gauge market's growth and risk expectations i.e. market sentiment, but I don't actually try to do valuation.
All I know is the discount rate should be higher than your opportunity cost of capital. How much higher is up to you.
Of course, there are textbook answers, which I'm not going to bother.
You can start with one of Van Tharp's books, available here at Pinggu. "Trade Your Way To Financial Freedom" is a classic. "Super Trader" is more recent, but the underlying principles are the same.