Summarized from the FreeBSD Handbook
Chapter 21.4 - Using 'make world'
------------------------------------
 1.) cvsup

 2.) check /usr/src/UPDATING and /etc/make.conf (for weird CFLAGS)

 3.) cd /usr/obj && chflags -R noschg * && rm -rf *

 4.) cd /usr/src && make -j4 buildworld

 5.) cd /usr/src && make buildkernel KERNCONF=mykernel

 6.) make installkernel KERNCONF=mykernel

 7.) SUGGESTED REBOOT TO SINGLE USER MODE (shutdown now)

 8.) mergemaster -p && cd /usr/src && make installworld

 9.) mergemaster

10.) REBOOT TO MULTI-USER MODE (shutdown -r now)


Notes on CFLAGS:
  - O2+ is known to fail in some instances. Probably shouldn't use it anyway.
  - CXXFLAGS is known to cause some compiles to fail. When in doubt, comment it out.
  - It's a good idea to build the base with pretty vanilla flags anyhow.