I3 Lense
As has been said on other threads, when you get them out, if your thumbs and the lense tabs are still intact put a little fairy liquid on each tab before you put it back in. This will make it a bit easier to put back in and easier to take out next time.
However, unless you have a really really really good reason to take the lense out (i.e. lense replacement), don't. It's more trouble than it's worth.