I'm not an experienced trader, so apologies if this is old-hat. I just stumbled across this today:
The Deflated Sharpe Ratio: Correcting for Selection Bias, Backtest Overfitting and Non-Normality

The author also gave a presentation on this, with the slides available here:
Deflating The Sharpe Ratio

I'm still digesting this, but it seems like it makes sense. I'd be interested your opinions and reactions.