I stumbled upon this a few weeks ago and it was so simple that I thought maybe everyone knew it but me. But when I asked a few people, they were surprised too.
If you want to zoom in on a particular item (a word, a picture, or other object.) using the mouse, hold down the CTRL key and roll the mouse wheel forward. To zoom out, hold down the CTRL key and roll the mouse wheel backwards. Easy!
I find this really helpful when working in Microsoft Publisher.