By default you have two options:
- Move your mouse over the volume control applet and scroll
- Hit whatever keyboard combination you have set to do the task
The reason I don't like these two options are that they require me to look at the screen/keyboard, instead of looking at whoever's talking to me, and when my laptop is closed (While I'm "studying") I have to first open the lid to do this.
In old Ubuntu you had a third option, move the volume control applet to one of the corners. Then you could simply move your mouse to that corner with a flick of the wrist, and scroll to change the volume.
In lucid however the new Indicator Applet system prevents you from customizing the location of the particular applets. As such I use CompizConfig Settings Manager to achieve the same result.
First install it:
sudo apt-get install compizconfig-settings-manager
From its main menu, select the Commands option
Set the first two commanad lines to:
amixer -c 0 sset PCM,0 20+
amixer -c 0 sset PCM,0 20-
Then you can set the corresponding button bindings, selecting whichever corner is comfortable for you, along with Mouse Button4 (Scroll up) for the first command and Button5 (Scroll down) for the second.
You should now be able to quickly change volume without looking. Note you may want to play around with different values, and also different channels. For example changing the command to "amixer -c 0 sset Master,0 5-" changes the Master channel by 5 (out of 255).
You could also customize other buttons in other corners to do other commands, but I leave it to you to explore the near infinite possibilities.