Too wide lines (hbox overfull)

In latex, lines are sometimes wider than the line length (hbox overfull error). One way to avoid it is to use the parameter: \tolerance. The parameter changes between 0 and 10000.

Latex: Citation Order for elsarticle

To order citations in your paper, you might want to use cite package like this:
\usepackage{cite}
However, as it was described here, the package conflicts with natbib package embedded into elsarticle.