How can I select which stocks to apply my system to?

Hi,
I am developing a set of trading rules that can be applied to say.. ftse100 stocks as well as US stocks.. etc.
How can I compile a list of the most traded stocks that take the clearest and biggest trends? I'm not looking for an outright answer as I know it cant be easy but it would be good if anyone can point me in the right way. So far I have been googling things like highest volume stocks and things like that. I am using IGIndex and in lists (for US) they have US Tech and Wall Street. I'm unsure how good these stocks are to trade (I'm used to UK stocks but at first glance these US ones take much nicer trends). Can anyone offer my any advice? please?

I apply Trend Strength Indicator, a naive way I have developed of comparing trends and confirming direction.

For TSI for EOD swing trading, convert your chart to weekly bars showing weekly H, L and C. Overlay the daily 50EMA and count the H, L or C points that are above the 50EMA out of the possible total over your selected time period. Convert this to a percentage I use a 33-week period, for reasons which will be obvious when you try it).

The method is a bit laborious, but makes it easy to compare and rank charts by predictability of trend, and, therefore, reduction of risk of being shaken out by volatility or reversal.