With the mechanical system I don't buy a lot of time, just 2 weeks or so. That keeps my cost down. I buy just out of the money or at the money.Right away I put in a limit price at a 30percent profit.  I watch the one hour chart. if the 5 moving average trend line starts moving against me I lower my price to a 20 percent profit.  That is as low as I ever go.

I never use stops, instead I use a straddle if the market moves against me.  This works for me because I never use more than 3 percent of my capital on any trade. This way I never lose sleep.  

I don't know if this is the way for anyone else. After 4 years of trading, this is my system that works for me.  hope it helps you.