How to add icon and screenshot for my app .deb package to see it in Ubuntu Software Center?
There are two questions here, the first is about the icon; this is actually provided by the app data package which has a pre-set number of defined icons. You can find it in:
/usr/share/app-install/icons/
But it won't help you put an icon in the software center. No custom packages have icons in the software center.
The second is about the screenshot. These can be added here:
How to include a screenshot of my application in the DEB/PPA to show it in Software-Center?