While you can use any timer (or timer app) you want, a dedicated Pomodoro app can make your life a little easier by automatically alternating between work and break periods. The 25-minute work session is long enough that you can stay fully engaged, while the 5-minute breaks, which are never too far off, give you a chance to check Twitter or your email without disrupting your work.
I'm using it right now to write this intro.
Despite how basic it sounds, the Pomodoro Technique is incredibly effective.
