studying brings happiness

If you use Google Reader for collecting and checking update news from your favorite blogs and websites, these shortcuts are useful.

m : make current item read or unread (I often use)
r : refresh
u : toggle full screen mode
v : opens the original source for this article in a new window
- : zoom out
= : zoom in (I like it)
...............

There are many keyboard shortcuts and not easy to remember all but I like to talk about some of them :

Ctrl++ enlarges text sizes ( I like it and often use it since big font size is better for my eyes )
Ctrl+- reduces text sizes
Ctrl+0 restores default text sizes
Ctrl+Shift+T opens the last closed tab ( sometimes I use )
Ctrl+T opens a new tab
Ctrl+N opens a new window
Ctrl+1 through 9 switches to a particular open tab position
...
see more shortcuts

Using keyboard shortcuts is quite interesting.