Open Terminal.
If you have brewed osxfuse installed, you have to uninstall it, because unsigned kexts are banned now. Type:
brew cask uninstall osxfuse
On the other hand, if you don't have Homebrew at all, download it:
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
Updating Homebrew is recommended.
brew update
If you don't have Homebrew Cask installed, type:
brew install caskroom/cask/brew-cask
Install a binary osxfuse package from Homebrew Cask:
brew cask install osxfuse
Install ntfs-3g:
brew install homebrew/fuse/ntfs-3g
You need to create a symlink for mount_ntfs, in order to make drives mount automatically:
sudo mv /sbin/mount_ntfs /sbin/mount_ntfs.original
sudo ln -s /usr/local/sbin/mount_ntfs /sbin/mount_ntfs
If you are running OS X 10.11 and the commands above fail, try:
sudo nvram boot-args="rootless=0"
edit: This doesn't work for me in the final El Capitan (from Mac App Store). I had to disable SIP through recovery. Could someone confirm that this is indeed necessary?
... and reboot your machine. Then try symlinking mount_ntfs again.