A good old fashion pair of human eyes is simply the best tool at your disposal for making these adjustments. Unfortunately, the peculiarities and unique qualities of each font cause perfect letter spacing to be quite difficult to hard program into software.

Why kern? The biggest rookie mistake you can make with typography is to assume that Illustrator, Photoshop, or any other app will spit out perfectly spaced type by default. Illustrator on the other hand is brilliant at displaying vector graphics at various levels of zoom (way zoomed out it gets a little messy but still better than Photoshop). Photoshop will show you a decent preview at 100% (Command+1) but at almost any other zoom level the text looks like crap and is not at all a good indication of what your final output will look like. As you can see, Photoshop is choppy and ugly while Illustrator is smooth and beautiful.

The left shows the Photoshop preview and the right shows the Illustrator preview.

This is a side-by-side comparison of two windows that I had open, each with a similar block of copy.

Typography illustrator