Mr. Krishnan,
The ideal time to buy straddles is when the vols. are low (you anticipate the vols to go up) so you don't shell out a ton for the premiums. Straddles are ideal for options that have 60 days or more to expiration so you give time time for the breakout to occur. To find great straddles :
Look for a consolidating market (wedge formation in price graphs)
Find if options are cheap (check Imp. Vol. relative to historical vol.)
Find if options have 60 days or more to expiration
Enter before the possible breakout (upcoming coming announcements, Govt. data, etc.)
Exit position 30 days to expiration (because of theta risk, an option loses 80% of its time value 2 weeks prior to expiration).
One good technical indicator to look for low vols. and price consolidation is bollinger bands. Look for bollinger bands that are contracting to a point where the daily range of the stock is close to touching both the upper bands and lower bands. This indicates that the stock is tightening and will propel itself into one direction. Happy Trading!