todays chart, page-73

Newbie question for the experienced traders/investors.

Yesterday I was sitting on over $5K profit and today it's gone after the SP fell 16%.

I like this stock and am thinking long term hold but I'm sad to see $5k gone from my account. I wish I could have taken the profit so that I can re-invest.

So how do you guys take profits when you do not know when the SP will fall?
Do you set trailing sell orders or set a value limit ?
If you are setting Trailing sell orders, what percentage/value do you use and what percentage of the stock would you sell? Do you sell all the shares?
I'm only new to investing and not sure how to go about this.
I would appreciate any tips with some examples or maybe point me to some online links
Thanks in advance