All files should be writable only by your user account. So the correct permissions for files and directories are:
- Directories: 755
- Files: 644
You may want to secure some files:
- wp-config.php: for maximum security, this file should be made writable by your user only or its group. This means 400 or 440 permission
- .htaccess: 666 permission, so that WordPress can automatically generate rewrite rules for you
- wp-content/: some plugins and themes may require write access to this directory. you will be prompted when necessary.
- wp-content/themes/: 664 permission if you want to use the theme editor
References: