I used to easily be able to take screenshots in the Ubuntu versions of mint by hitting Ctrl-Prt Scrn on my keyboard. This didn't work in LMDE though, but it's an easy fix.
Open your menu to Preferences > keyboard shortcuts
Click the add button at bottom
Type Screenshot under name
for command type: gnome-screenshot
Once you click done, then just hit the key combination you want to assign to it and you should see it assign that keystroke to the entry you just made
Now just use your key shortcut and choose a place to save the file. Easy as Pie.