Log on to the Ticketmaster website, and open a free account by filling out the informational fields.
Enter "Coldplay" in the search engine, and click on the band's name under a heading which will read either "Events Scheduled," or "No Events Scheduled."
Click on the bar which reads "Add To Favorites." This feature will send an email notification that Coldplay will be playing near you before the tickets go on sale.
Go to the official Coldplay band website, Coldplay.com, and go the section of their site devoted to upcoming live performances. Click on the "mailing list" icon at the bottom of the page, and fill out the informational fields. As with Ticketmaster, this feature will notify you of performances coming to your area before tickets go on sale.
Check your emails regularly, and call Ticketmaster to order tickets as soon as you've received the email. Have your debit or credit card out and ready to use, as concerts by popular bands have been known to sell out in minutes.