Photoshop is an image program and doesn't do text extremely well. You will often find that the text is either jagged or even sometimes blurry. Check your DPI. If it's low, try turning it up to 300. It also depends on the size of the file your working with.
Ultimately you may wish to move it over to Illustrator, smooth the text and then reimport it to Photoshop. Or if you can, do the whole file in Illustrator