While ago I was trading CSCO in relations to $COMPX. Why? Their charts where identical. I just put charts on top of ech other on ten screen. In many cases $compx chart indicated earlier move on CSCO. I did nothing with advansing /decl just traded based on Stochasticks, MACD and the charts themself (1-min 5-min and 30-min). It was fun for a while.

Then i just switched to QQQ and abandoned stocks all together (why bother?).

I would recommend to identify the most influential stocks for the group or index and see how the charts correspond.