Valo, Good to see you found our sell discipline page on Geo. It is well hidden!!! http://geoinvesting.com/about/investmentdisciplines.aspx

I have found that the best sell discipline approach is some form of the methodical rule. How much you sell at the 20% market will depend on your risk assessment of the market as well as how much you like the company.  For example, in 2009 i tried to ride stocks as much as i could before selling and very little early in the rise. I have employed that same rule since September of 2010.  Also, the more you like the stock, the less you sell at 20%. 20% to 50% sell at 20% is the sweet spot.  

Ideally, I like to have two portfolios:

One that uses just the 20% rule with high concentrations in few companies. i would keep this port small and reduce the size once it reaches certain level. for example, let's say you start with 5k.. At about $50k, I would reduce to $25K.. so your sweet spot will be 25K to 50K..

The other that uses the methodical approach.

I have been a little messy lately and will stick some limits in next week using the methodical rule..