Average P/E of Nifty from 01-Jan-99 till today is 17.66 and this one is one of the most important factor which we all should take into account while deciding to sell your holding. During the peaks of 2001 and 2008 Nifty P/E was more than 28 and market crashed after that. Currently P/E is hovering around 18-20 which are cautious levels.

Thanks.