How to hide all your HUDs (temporarily)

The Second Life viewer has a handy built-in feature which allows you to hide your HUDs from your screen. This is only a cosmetic operation, as the HUDs will still be equipped and working as normal.

There are two ways to achieve this. Since Viewer 3, Linden Labs has added a handy dandy shortcut called Show HUD Attachments to the Me menu, which is the first menu at the top (left) of your viewer. You can also use the following keyboard shortcut to achieve this effect:
Alt + Shift + H

I recommend to not use this functionality as a way to hide lots of HUDs. While invisible, these items still require server resources and contribute to lag. Instead, try to detach as many HUDs as possible. Personally I’ve found that the only HUD I never take off is my AO, everything else can be derezzed ’till needed.

Link

The Advanced Menu

The Advanced menu is a menu in the Second Life Viewer which is hidden by default. A lot of nice tips, tricks and tweaks directly or indirectly involve the use of this menu. I’ll explain a couple down later on the blog. Below you’ll find a link to the official documentation.

All about the Advanced menu on the official Second Life Wiki*

*Just want to know how to make this menu appear? You can enable it through the Advanced tab in Preferences or use this keyboard shortcut to activate the menu:
Ctrl + Alt + Shift + D