Ravi C It needs time, not difficult one you get the technique. For those who are doing headstand the first time, the tips are as follows-
Give a push from feet to get the initial lift off the ground and then push hard on your elbows but not on your neck (there should be no pressure in the neck).
Use your back muscles to raise yourself further from the ground instead of trying to use leg muscles. Dont fear falling but focus on back muscles.
For those who can already do headstand for less than 5 mins, the key is to relax and not think about it. Breathe naturally.
you will do it more than 5 mins without realizing when you are relaxed and breathing naturally.
Good Luck Guys :)