You should start off treating the engine very gently i.e. gentle revs and never more than 1/4 throttle. Over time you gradually use more revs and more throttle until you eventually end up using the full range of the engine. It is important to eventually end up using all the power and rev range to wear harden various parts. It is also important that you do not keep to a single continuous speed or gear but vary your speed quite a bit during this time (a long highway journey is NOT a good break in if you just sit in Top Gear at a continuous speed). This is because things are still hardening up and you can wear a groove into them.
Modern engines break in relatively quickly, often 1000km, older designs took longer as the tolerances were not as precise. The first oil change is often a lot sooner than later ones as during break in rough edges from manufacturing will be worn off and end up in the oil.
Here is more advice from various contributors:
Breakin' in a Brand New Broken Heart was created in 1961-04.
no. there is no breakin period for gas powered RC
Breakin' Out was created in 1987.
The duration of Breakin' is 1.5 hours.
If it is brand new - no. But - things do go wrong for whatever reason. New car should have a warranty.
Breakin' Dishes was created in 2006.
Breakin' - song - was created in 2003.
Breakin' the Funk was created in 1979.
Breakin' was created on 1984-05-04.
Breakin' Convention was created in 2004.
Breakin' the Chainz was created in 2005.
Breakin' Down was created in 1995.