Prints and Charging Prices

Hi all, I know this has been asked a million times, but I have done searches and even ordered the book Photgraphy Pricing. The book doesn't say anything from what I have read so far about pricing individual photos.
I have some photos I have done that are being wanted in a 20x24. I don't know if this is a good size or not. I have never done larger than 16x20. My main ? is what to charge and and what is better 20x30 or 20x24. I need to get some starting price info for anything from a 4x6 to 20x30. Does anyone have any good advice, books etc. Thanks for the patience and help in advance.

Brittany

Are you printing these yourself? Or having a lab do them and then you are selling the finished prints?

I am having lab print and then I am selling the finished prints, yes

What do you mean 'good size' and 'which is better'?

If your picture is cropped to how it should be then print it like that, and use a matt. I wouldnt crop a picture to match the paper size, I would always match the paper size (and leave a border, if nessecary) to the print.