How can I develop a custom theme from scratch? I wonder how to develop a custom theme from scratch. I understand the overall structure of Drupal theme. I've created an .info file and enabled the theme through the admin interface, but I get a blank screen.

I haven't yet coded any of the theme files. I'm unable to define html.tpl.php, page.tpl.php, node.tpl.php, region.tpl.php.

I do have empty css, js and images folders. In my templates folder I've an empty html.tpl.php, page.tpl.php, node.tpl.php, region.tpl.php, field.tpl.php.

Any suggestions?
Hello World

It seems that the current version of your theme works as designed: empty templates that result in a blank screen, that's exactly what "I" would expect. Try adding "Hello Umair" in any of those empty files, and see what you get next.

Start from an example

A much more effective approach however might be as suggested by longboardnode : copy from whatever theme you like, and apply the "same-as-except"-strategy. 

Start from a base theme

Or maybe create a subtheme from your favorite base-theme (Omega, Zen, Bootstrap, ... there are plenty to pick from).

Follow the instructions in the documentation

An extremely basic example you may want to look at: Create a new custom theme with CSS alone. And if you're ready for it, study the Theming guide, especially the Theming Drupal 6 and 7 child pages of it.