first off best for you too post questions like that after market - otherwise these get buried and we are busying trading but here you go read this

The general theme is 5% of total if you read the books, however what I like betteris calculating the amount I'm willing to risk on the position, which I can calculate using the price difference from my entry too my stop in order to calculate the amount of shares I'm buying or shorting. Nothing to do with the total amount of my account 

For example if I see a pattern like a falling wedge, or bull flag and my entry is going to be $20, and I see a higher low stop at 18.5 where I'm willing to place my stop, that's $1.5

so if I'm willing to risk $300 on the trade that's 300/1.5 = 200 shares. That means I can buy 200 shares of that stock because of my stop gets hit I lose $300, that's what I was willing to risk and so that's the amount of shares I should buy. I don't care what % of my account those 200 shares represent.

Has NOTHINGto do with what % of my account those 200 shares represents. at times it might be 1% or 15% if I have a ridiculously tight stop where I can go heavy in shares but risk very little because of tight stop. I base my trades on what I'm willing to risk.

This is a good practice because it FORCES you guys to know your exits, forces you to have an exit plan, which is always the most important. Too many folks buy a stock and then worry about an exit plan later-  this forces you to have an exit plan before you even enter the trade because you are using that stop out exit to calculate your position size