General waiting list (GNWL) is favoured over tatkal waiting list (CKWL) at the time of chart preparation as per this indian railway circular. Therefore, booking of confirmed tatkal ticket is of utmost importance as waiting list tatkal ticket has very less chances of confirmation and tatkal tickets do not go through RAC. Following tips will help you in booking confirm ticket in tatkal quota through irctc website:

• Create more than one credentials for logging on to irctc website. If you have only one login details, borrow one from your friend or family. Trying to book ticket parallely using multiple browser/computer always increases chances of getting a tatkal ticket. DO NOT use same irctc login details on multiple browsers simultaneously as irctc can detect it and log you out from all sessions.
• Make sure tatkal quota for your journey opens one day in advance. It might open two or more days in advance, if the train reaches your boarding station on second or more days of its running. For example, if you want to book tatkal ticket from Nagpur to chennai in Chennai Rajdhani Express (12434), the tatkal booking opens 2 days in advance in this case from your journey date as the train reaches Nagpur on 2nd day of running.
• Keep Id card details such as PAN card or driving license of one of the passengers handy. This way you do not have to search for it after you have started the booking process.
• Save some time by entering passenger details beforehand. Fill passenger details before 10am for ac class and before 11am for non-ac class, you need not fill them again and save a couple of minutes this way which increases your probability of getting confirmed tatkal ticket. This is how you should do so:
  • Login into the irctc website 5-10 minutes ago and do these before 10am for ac ticket and 11am for non-ac ticket.
  • Select origin destination, choose date as today’s date and enter ticket type and click on ‘Find Trains’. Now select quota as TATKAL and click on BOOK NOW for today’s date for any train.
  • Enter passenger details including id card details and mobile number. Now instead of clicking on ‘Next’ which will take you to payment, click on ‘Replan’ which takes to back to the ‘Plan My Journey’ page.
  • Exactly at 10am (or at 11am for FC, SL and 2S) put your correct journey date and try booking. When you come on Passenger Details page, you will see that all the details which you entered before are still there. So just enter the captcha and click on ‘Next’ for payment.
• For AC classes, try booking in 2A (second ac) first. For most of the routes, 2A gets filled less quickly than 3A inspite of lesser berths.
• Avoid trying to book ticket on trains for which tatkal tickets have already exhausted. Keep checking parallely current berth availability for tatkal quota on trainman.
• Make payment using netbanking (preferable by HDFC or ICICI bank) as this is the fastest mode of payment. If you choose to pay by cards you need to enter long card numbers and lot of other details which takes time. Since irctc has made OTP verification mandatory so one should keep their phone nearby to get OTP details from phone.
• If you are not able to book tatkal ticket for ac classes, you can try your luck for non-ac classes at 11am again.

Source : trainman