clear internal memory
GO to manage applications and within each app you have the option to "clear cache".
I didn't want to root my phone but I find the best way to free up a reasonable amount of space is to "uninstall updates" on those preinstalled apps that cannot be moved onto the sd card e.g maps and gmail. For all they don't seem that big, I can usually free up about 20mb that way. Trouble is they reinstall automatically every so often - so if anyone can tell me how to stop that? I keep thinking I have then it happens again. And I suppose if you use maps then its not necessarily the best solution!