As mentioned above, clear your internet browser caches and temp files from Main Storage Memory, and make sure to set your attachments and caches to save to micro SD card. Also, consider installing ClearTemp, it's freeware that you can install to help free up main storage as well as much more.
Check out this thread link for more tips:
http://forum.ppcgeeks.com/showthread.php?t=111584
Here's a link for latest version of ClearTemp (v1.3) by Developer Vicott Wong:
http://www.4shared.com/file/23212293...rTemp_v13.html
Hope this helps,
R