prepare disk & make filesystem
mount /dev/sdaX /mnt/gentoo

extract stage3 & portage tree
tar -xjpvf stage3-xxx.tar.bz2 -C /mnt/gentoo
tar -xjvf portage-xxx.tar.bz2 -C /mnt/gentoo/usr

copy DNS info
cp -L /etc/resolv.conf /mnt/gentoo/etc/resolv.conf

mount -t proc none /mnt/gentoo/proc
mount -o bind /dev /mnt/gentoo/dev
cp /proc/mounts /mnt/gentoo/etc/mtab

chroot /mnt/gentoo /bin/bash
env-update ; source /etc/profile

emerge metadata

ln -s /usr/share/zoneinfo/Asia/Shanghai /etc/localtime

Configuring the USE Flags, Portage Options(use,keywords,etc.),
and Compile Options(cflag,etc.): /etc/portage/make.conf
update the make.conf with Optimize
CFLAGS="-O2 -march=native -fomit-frame-pointer -pipe"
CXXFLAGS="${CFLAGS}"

Usefull tools
emerge rsyslog grub vixie-cron sysfsutils gentoolkit portage-utils acpid

bootloader & change root password
emerge grub
passwd

Make a kernel and up you system
emerge gentoo-sources