About shaping the Drupal "add content" pages My question is that do you change the Drupal "add content" pages appearance and fields for your final version of project?

Actually, I really do not know how it is conventionally provided for Drupal customers. If you customize those pages, how do you do it?

Thanks
I like to work with Panels to customize the Add content pages. I'll write down a small step by step tutorial to give you a starting point and maybe a better understanding how to module works if you are not familiar with it.

Once you have Panels installed you navigate to » Administration » Structure » Pages in the menu. Then enable the Node add/edit form variant.



When the variant is enabled click Edit and then Add a new variant. Click Create variant, choose layout and click continue on the next step click continue.

Now add the form elements you want in the respective regions by clicking the cog wheel in the top left corner of the region.



Under the category Form you will find all form elements.

In the example below I've added the title and body field to the left and the menu settings and the submit button to the right.



Under selection rules in your panel you can say that this variant is valid for the content type "Page" for example and have another layout/setup for other content types. If you don't add a selection rule the variant will take over the content creation page for all content types.

You can add new Panel layouts to a module/theme if the standard provided doesn't work out for you. 

A gotcha
One small gotcha I've experienced is that if a field is not placed in the panel, let's say an image field. And you re-save existing content it will remove the image from the node. When the node is saved the submit function interprets the value as empty. To avoid this add the pane General form to one of your regions and click the cog wheel for the pane and css properties. Under css class enter element-invisible. This way all form elements are present but hidden by css to avoid the missing image situation :)