I am trying to theme node page based on content type. Here I tried to follow the instructions as in http://drupal.org/node/249726.
What I did , copied node.tpl.php file to my theme directory. Renamed it as page-node-mycontenttype.tpl.php and wrote preprocess function in my template file as shown in above link.
Apparently found that It displays only the Node contents but not the common layout elements(HTML) (logo,header, footer and sidebars etc. which is defined in page.tpl.php).
So is it necessary for me to define same common layout elements(HTML) once again (those defines in page.tpl.php) in page-node-mycontenttype.tpl.php?
If so then I have to manage 2 template files. Any HTML changes need to be done twice in both template files.
Is there any better way of having common layout template file referred by both page and node content type only the middle content area is coming from two different files (page or node content type)?
Could you please suggest common practice and way to achieve this?
Note: Make sure that to override node template file with respect to content type then both template files node.tpl.php and node-[content_type].tpl.php file need to be in your theme directory.
The file you're looking for is node-mycontenttype.tpl.php . You want a node template, not a page template. If you rename page-node-mycontenttype.tpl.php to node-mycontenttype.tpl.php, you'll get the result you're expecting.
The page template (page.tpl.php) in Drupal defines the overall markup and where the contents of the various regions will be outputted. Traditionally it includes the logo, menu, footer message, and a few other static elements. The Drupal theme system allows you to override the entire page template for a specific node type (which is what you ended up doing), but based on your explanation, what you're really trying to do is override just the node template.
Further reading: Explanation & diagram of what files control which pieces of output: http://drupal.org/node/171194 General documentation on overriding output in the theme system: http://drupal.org/node/341628
When reading the above, make sure to note the version of Drupal that it applies to (there's a tag up at the top of each page). Things changed fairly dramatically between 5 and 6 and have shifted again (though not nearly as much) between 6 and 7.