Make note of the book's call number - jot it down, take a photo with your cell phone, etc. Make sure the book is listed as being available.
We'll use The Book of Phoenix as our example; it's available, and its call number is PS3615.K67 B66 2015.
Go to the appropriate floor. According to the library catalog, The Book of Phoenix is on the third floor. (This is where most of our books are.)
If you take the stairs to the third floor, you can look at the signs on the doors (see the image below) to figure out which one to take. If you took the elevator, make a left.
Look at the signs on each shelf - find the range that includes your call number.
Sometimes, it may seem like there is a gap in the call numbers. For example, the shelf in the left photo has the call numbers PS3568 .O248 M9 1978 through PS3570 .A48 Z69 1998. Our call number doesn't fit in this range. However, the shelf right next to it has the call numbers PS3618 .A3475 B57 2014 through PT1898 .W4 1965 v.2. Shouldn't our book be somewhere in between these two?
If you encounter something like this, proceed down the aisle - you'll see another row of shelves with their own signs. In the photo below, we found another aisle with the call number range PS3573 .I449 A6 1975 through PS3617 .U584 T48 2010. Our example book should be here.
Look on the shelves for your call number. If for some reason you can't find it, let a library employee know!