Ahhhh tables — one of the infuriating things with tables in LaTeX, is that sometimes they’re so wide that they extend into the right margin, or even off the page. Here are a few things I usually do to deal with them.

Use tabularx to auto-wrap long column contents

Sometimes you have a column where the lines are long, but by default, lines in a table row don’t wrap. You can either use the makecell trick to manually break the lines; or you can make text in that particular column line-wrap automatically, by using a p{3cm} column specifier (but then you need to experiment a few times for a right width), or by using the tabularx package.

\usepackage{tabularx}
...
% Contents in the second and third columns will be auto-wrapped,
% so that the entire table will fit the text width nicely
\begin{tabularx}{\textwidth}{l X X l}
No. & These are long statements... 
    & These are very long too... 
    & 0\\
...
\end{tabularx}

Use makecell to quickly break a cell into multiple lines

Sometimes you have a column with narrow values (e.g. just ‘34’, ‘67’…) but the column heading is long (e.g. ‘No. of patients’, which makes the column use up too much space. In this case you can use the makecell package, and then manually line-break the column heading:

\makecell{No. of\\patients} & Region & .... \\
% Note that All of the above are still on the same table row.

Reduce the column paddings

So in some situations you can get away with making the inter-column separation or padding smaller:

\begin{table}[hbt!]
\setlength{\tabcolsep}{4pt} %% default is 6pt
\begin{tabular}....

Possibly the simplest but not always appropriate: just make the whole table use a smaller font. (but not usually recommended!! make sure your table is still readable.)

{\small % (or \footnotesize if still readable)
    \begin{tabular}
    ...
    \end{tabular}
}

Do check that you have the pair of braces around the \small and the tabular. Take care that the table contents can still be read comfortably, and that your university or publisher allows you to change the font size in tables!

Let LaTeX shrink the entire table to text width. (not recommended at all!!)

\resizebox{\textwidth}{!}{%
    \begin{tabular}
    ...
    \end{tabular}
}

Rather than figuring out whether a \small or \footnote will be enough ourselves, LaTeX will treat the entire table as a box, and try to resize it so that it fits the text width exactly. Again: take care that your reader can still read the shrunk table, and that it’s allowed by your university or publisher. From a LaTeX best-practice point of view, this approach is really not recommended.

Make the table landscape

There are a few different ways of doing this — try for example the sidewaystable environment from the rotating package:

\usepackage{rotating}
...
\begin{sidewaystable}
\caption{...}
\begin{tabular}
...
\end{tabular}
\end{sidewaystable}

And always remember: rather than agonising over how to fit a table on the page, it’s often more useful to consider how to present the data so that the reader can access and understand it easily!