Example 1 Arrange the four fractions $-\frac{1991}{1992} 、-\frac{91}{92} 、-\frac{1992}{1993} 、-\frac{92}{93}$ in ascending order: $\qquad$
$$
\begin{array}{l}
-\frac{1991}{1992}+1=\frac{1}{1992}, \\
-\frac{91}{92}+1=\frac{1}{92}, \\
-\frac{1992}{1993}+1=\frac{1}{1993}, \\
-\frac{92}{93}+1=\frac{1}{93}. \\
\text { And } \frac{1}{1993}<\frac{1}{1992}<\frac{1}{93}<\frac{1}{92}, \text { so } \\
-\frac{1992}{1993}<-\frac{1991}{1992}<-\frac{92}{93}<-\frac{91}{92}.
\end{array}
$$