What are your techniques to make what's below look better? Thanks.
\documentclass{article}
\usepackage{amsmath}
\newcommand{\ud}{\mathop{\mathrm{{}d}}\mathopen{}}
\begin{document}
\begin{equation}\everymath{\displaystyle}\begin{pmatrix} \ud X_1
\\ \ud X_2 \\ \ud X_3
\end{pmatrix}=\begin{pmatrix} \ud x_1 \\ \ud x_2
\\\ud x_3 \end{pmatrix}+\begin{bmatrix}
\frac{\partial u_1}{\partial x_1} & \frac{\partial u_1}{\partial x_2} &
\frac{\partial u_1}{\partial x_3} \\
\frac{\partial u_2}{\partial x_1} & \frac{\partial u_2}{\partial x_2} &
\frac{\partial u_2}{\partial x_3} \\
\frac{\partial u_3}{\partial x_1} & \frac{\partial u_3}{\partial
x_2} & \frac{\partial u_3}{\partial x_3}
\end{bmatrix}\begin{pmatrix} \ud x_1 \\ \ud x_2 \\
\ud x_3 \end{pmatrix}
\end{equation}
\end{document}