How to order citations by appearance using BibTeX?

There are three good answers to this question.

• Use the unsrt bibliography style, if you're happy with its formatting otherwise
• Use the makebst (link) tool to design your own bibliography style

And my personal recommendation:

• Use the biblatex package (link). It's the most complete and flexible bibliography tool in the LaTeX world.

Using biblatex, you'd write something like

\documentclass[12pt]{article}
\usepackage[sorting=none]{biblatex}
\bibliography{journals,phd-references} % Where journals.bib and phd-references.bib are BibTeX databases
\begin{document}
\cite{robertson2007}
\cite{earnshaw1842}
\printbibliography
\end{document}

The best I came up with is using the unsrt style, which seems to be a tweaked plain style. i.e.

\bibliographystyle{unsrt}
\bibliography{bibliography}

However what if my style is not the default?

You answered your own question---unsrt is to be used when you want references to ne listed in the order of appeareance.

But you might also want to have a look at natbib, an extremely flexible citation package. I can not imagine living without it.

Add this if you want the number of citations to appear in order in the document they will only be unsorted in the reference page:

\bibliographystyle{unsrt}

I used the following in overleaf and become in ascending order:

\usepackage{cite}

\bibliographystyle{unsrt}

with unsrt the problem is the format. use \bibliographystyle{ieeetr} to get refences in order of citation in document.