I want to start making wordpress themes. Please tell me how can I start that keeping in view the requirement of current market demand.
I'll be honest here. If you don't know where to start you're gonna have an extremely hard time. You need to be able to solve simple problems like the one you currently have to stand a chance with the horror of wordpress backend.
Here is a good place to start http://code.tutsplus.com/series/developing-your-first-wordpress-theme--wp-33845 They also have a membership for $15 a month with video tutorials on wordpress web design and development. You should also look at learning some basic html and css skills. You can also use bootstrap framework to create your themes. Has for what's hot & selling in wordpress themes try looking what selling in marketmarketplaces like themeforest. Hope that helps!
I think the best place to start is YouTube. Try these Free courses. Very useful for beginners. https://www.youtube.com/user/LearnWebCode/playlists https://www.youtube.com/user/easydevtuts/playlists Or paid services like @rhodygossip mentioned, beside "tutsplus" i would recommend: http://teamtreehouse.com/library/wordpress-theme-development
If you want to develop wordpress theme than you first need to learn PSD to HTML and then wordpress theme development. You also need to learn basic wordpress. I think Video tutorial is the best way to learn wordpress. You can search on YouTube and you will find a huge collection of wordpress videos.
The first thing you should do is look at popular Wordpress themes now and see what is popular. What design elements are popular? What features are popular? And then plan to incorporate those things into your designs. Then you must verse yourself in the intricacies of Wordpress. You must understand themes, custom pages, the template hierarchy, where to look for function reference, and more. For design insipration, see: https://wordpress.org/themes/ ThemeForest.net ElegantThemes.com Themify.me (If anyone else has any sites that offer Wordpress themes, feel free to list them.) Information you should know about developing for Wordpress https://codex.wordpress.org/Theme_Development http://codex.wordpress.org/Template_Hierarchy http://codex.wordpress.org/Creating_a_Static_Front_Page https://codex.wordpress.org/Theme_Customization_API http://codex.wordpress.org/Pages http://codex.wordpress.org/Page_Templates http://codex.wordpress.org/Functions_File_Explained http://codex.wordpress.org/Function_Reference http://codex.wordpress.org/Writing_a_Plugin http://codex.wordpress.org/Plugin_API
It is great that you are starting a wordpress themes designing, for choosing a new wordpress themes there are several free wordpress themes which are a great way to get a blog or website off the ground. With website you can also provide customers to the great seo services and offers, there are some sites which provides you the new theme for wordpress designing like InterStellar, Arcade, vFlex, Appliance, Zenith, Noteworthy etc.