Kenneth R. Marks of The Ancestor Hunt website has a very good tutorial on researching city directories at the Internet Archive. It is posted at YouTube and is free to access:
To watch a bigger (screen-wise) version of this video, click on the "play" button above, then click on the YouTube icon that will appear at the bottom of the video. This will take you to the YouTube site to see a larger screen.
Ken also has a number of tutorials on newspaper research on his site.