How to set proper permissions for Magento on server?

Question

I'm getting lot of issues with permissions.

In magento admin panel:

Your web server is configured incorrectly. As a result, configuration files with sensitive information are accessible from the outside. Please contact your hosting provider.

When I upload images from cms:

The directory is not writable by server.

If anyone access this url: http://example.com/app/etc/modules/

they can see easily configuration settings.

Using FTP account: I'm not able to override any file and some times I'm not able copy any local folder to server through FTP.

My application place is /var/www/html.

with senior developer advice I execute following commands:

find <foldername> -type d -exec chmod 755 {} \; 
find <foldername> -type f -exec chmod 664 {} \;

and below are present permissions for each folder.

drwxr-xr-x 12 root     root     4096 Jun 10 13:06 var
drwxr-xr-x  3 root     root     4096 Jun 10 13:06 www
drwxr-xr-x 15 www-data www-data 4096 Jun 18 07:29 html

root@web-server-magento:/var/www/html# ls -l

total 14644
-rw-rw-r--  1 www-data www-data     2834 Nov 26  2013 api.php
drwxr-xr-x  6 www-data www-data     4096 Jun 17 11:16 app
-rw-rw-r--  1 www-data www-data     2831 Nov 26  2013 cron.php
-rw-rw-r--  1 www-data www-data      717 Nov 26  2013 cron.sh
-rw-rw-r--  1 www-data www-data  2454234 Oct 26  2011 data.sql
drwxr-xr-x  8 www-data www-data     4096 Jun 11 07:21 downloader
drwxr-xr-x  3 www-data www-data     4096 Nov 26  2013 errors
-rw-rw-r--  1 www-data www-data     1150 Nov 26  2013 favicon.ico
-rw-rw-r--  1 www-data www-data     5979 Nov 26  2013 get.php
drwxr-xr-x  2 www-data www-data     4096 Nov 26  2013 includes
-rw-rw-r--  1 www-data www-data    11510 Jun 10 13:06 index1.html
-rw-rw-r--  1 www-data www-data     2642 Nov 26  2013 index.php
-rw-rw-r--  1 www-data www-data     2366 Nov 26  2013 index.php.sample
-rw-rw-r--  1 www-data www-data     6441 Nov 26  2013 install.php
drwxr-xr-x 12 www-data www-data     4096 Jun 18 06:28 js
drwxr-xr-x 13 www-data www-data     4096 Nov 26  2013 lib
-rw-rw-r--  1 www-data www-data    10421 Nov 26  2013 LICENSE_AFL.txt
-rw-rw-r--  1 www-data www-data    10679 Nov 26  2013 LICENSE.html
-rw-rw-r--  1 www-data www-data    10410 Nov 26  2013 LICENSE.txt
-rw-rw-r--  1 www-data www-data    10327 Jun 11 14:48 logo.png
-rw-rw-r--  1 www-data www-data     1319 Nov 26  2013 mage
drwxr-xr-x 13 www-data www-data     4096 Jun 18 07:29 media
-rw-rw-r--  1 www-data www-data      886 Nov 26  2013 php.ini.sample
drwxr-xr-x  2 www-data www-data     4096 Nov 26  2013 pkginfo
-rw-rw-r--  1 www-data www-data   585086 Nov 26  2013 RELEASE_NOTES.txt
drwxr-xr-x  2 www-data www-data     4096 Nov 26  2013 shell
drwxr-xr-x  5 www-data www-data     4096 Nov 26  2013 skin
drwxr-xr-x  9 www-data www-data     4096 Jun 18 06:57 var

Please comment if any extra information needed.