There are a few query parameters you can use to quickly access pages or modes in Sitecore. I'll list down some of the queries I often use when working with Sitecore.

1. sc_mode - I use this to quickly change the display mode of the website. I can easily switch to experience editor mode by specifying sc_mode=edit and go back to normal view by sc_mode=normal.

• normal – normal website view
• edit – page editor mode
• preview – preview mode

2. sc_site - Sitecore can host multiple sites. I can switch between sites using sc_site=MySiteName. MySiteName is the site name added in the sitecore config.

3. sc_lang - Switching between languages can be as easy as adding sc_lang=fr-FR.

4. sc_itemid - I can directly access a page by its id with parameter sc_itemid={11111111-2222-3333-4444-ABC123POE}.

5. sc_database - If you want to check if a change has already been published to the web database you can switch database using sc_database=web and go back using sc_database=master.

There are other useful queries although these are the ones I often use. 

Let me know in the comments if you know other useful query parameters.

Cheers!