Make Title and Section Headings

In your document's preamble, include the following commands:

\title{Your Title}
\author{Your Name}

After beginning your document, include the \maketitle command. In HTML, the Title will become a heading level 1, which is the top level of your heading hierarchy. 

The \section{} and \subsection{} commands can also be used to add heading levels 2 and 3, respectively.

Write Alt Text for Images

Write alt text for your image using the alt argument of the \includegraphics{} command. For example:

\includegraphics[alt={Line graph of f(x)}]{chart.png}

For data visualizations, your alt text should be a short description that identifies the chart type and purpose.

Add Data Tables after Charts

Data tables provide an accessible way for screen reader users to navigate and understand data; they act as your "long description". Always include headers and a caption with your table. For example:

\begin{table}[!h]
\centering
\begin{tabular}{|c|c|}
\hline
\textbf{y} & \textbf{x} \\
\hline
1 & -1 \\
0 & 0 \\
1 & 1 \\
\hline
\end{tabular}
\caption{f(x)}
\end{table}

Convert to HTML and MathML

Since the PDFs produced by TeX engines are not accessible, you should provide an accessible alternative in the form of HTML and MathML.

Pandoc and LaTeXML both offer free webapps that allow you to upload your TeX document and output an HTML file.