How to bowl a "Doosra" in the game of cricket?

Its seems to be very easy/smooth/effortless but arduous to deliver like Saqlain Mushtaq . But not impossible required more effort and skill(practice).

Hold the ball like a fast bowler normally would, with the index and middle fingers on either side of the seam. For better ball control, the index finger should just about touch the seam. The thumb may rest on the ball but usually does not contribute to delivery. The remaining two fingers are used to hold the ball in place. The run-up involved in bowling the doosra is the same as in a normal off-break.

*It's possible to bowl doosra legally: *

Read more at: http://timesofindia.indiatimes.com/articleshow/38660280.cms?utm_source=contentofinterest&utm_medium=text&utm_campaign=cppst

Reference: https://www.thenational.ae/sport/doosra-can-easily-be-delivered-within-the-rules-contends-mushtaq-1.237419