I kind of like Big Jim's comment about telling a story.
If these are your lyrics, don't beat yourself up if the words aren't perfect every time, just be sure the story remains consistent.

My other thought goes back to the basics.
Think about when you have the words printed in front of you. When you are singing, you are reading ahead so you know what's coming up next.
When singing from memory, the only time you have is when you breathe between verses, don't spend that time thinking about the quality of what you just sang; instead, read ahead in your mind to what the next verse will bring. If you keep your mind ahead of your lips, the words will be sitting on your tounge waiting for the chance to spill out.

Just remember. You can't change what you've already sung, but you still have the opportunity to affect the delivery of your next line. Put your money there.

Hope this helps.

If music be the food of love, why is it so hard to keep my family fed?

Pete
http://www.soundclick.com/bands/pageartist.cfm?bandID=734566
http://cwmusicpf.zoomshare.com/