For me, Topcoder is a very exciting full-time job that I still love after 5 years.
Getting qualified for TCO finals several years in a row.
Math, Algorithms, Yoga, Swimming, Playing with pets.
Complete your first challenge no matter what, even if the other registrants are experienced and they will most likely win. Don't get discouraged, consider the first challenge as a way to get familiar with the project. You'll gain a lot of confidence after the first one.
I mainly compete in Assembly and Code challenges nowadays and try to compete in as many SRMs I can. I got qualified for TCO in 2013 and 2014.