For example when there has been some consolidation and the volume has been relatively low, and then as you watch the stock you see the volume starts to rise and the price reacts and breaks out, at this moment you know how the bigger picture looks like, you know that there are some important levels in the larger timeframes, you know how the sector and related stocks stand, you see that the price gathers inertia and just blasts through that levels... that's what I call a potential activity. If you are lucky, the activity is for real, it turns out (in hindsight) that some large players were involved in the stock, then the public, but since you recognized the initial move as a potential opportunity, you took the risk and positioned yourself early and you just watched the stock move in a straight line and all you had to do was to wait patiently for one or two corrections and get out as the price climaxes
If you are asking if I am using some special tool to spot activity, I don't. I just watch a list of stocks, sometimes their charts look like a mess and you have no idea where they are going. But then you see something, draw some trendlines, and start to watch closer. Once they break the lines, you put your finger on the trigger and wait...
The difficult part is not to do anything, when there is nothing to do and to get out of the stock if the move is not what you expected.