Thats really a tough question...!! Getting Tatkal ticket in Rajdhani that too in peak season is like climbing everest.
Btw for it, u can go for 3 basic things:
1. Hi speed internet connection, so that irctc works fast and can be able to book by 10:03 10:05 max. OR
2. Go to prs counter and try to be in first five atleast. OR...
more...
3. Ask an agent who can ensure u for same.
Still, Good Luck !! :)