Consider this equation:
first $\lceil (cN-n) |S_{n+1}|\rceil$ points
which renders to:

Is there a way to improve this, from the perspective of readability? The only improvement I could suggest is:
first $\lceil\, (cN-n) |S_{n+1}|\,\rceil$ points
which renders to:

I believe it would even better to read, if the interior of the ceiling would be shrinked only a bit, so the ceiling delimiters are a bit higher.
\documentclass{article}
\begin{document}
first $\lceil\, (cN-n) |S_{n+1}|\,\rceil$ points
\end{document}
Edit: replaced minimal class with article, as suggested by egreg.

\_ceils and introducing a little space before the\rceiland in between)and|. I'd omit extra spacing before(because this glyph is already curved away from the\lceila bit.first $\bigl\lceil (cN-n)\, |S_{n+1}| \,\bigr\rceil$ points. Consider reading chapter 18 of the TeXbook "Fine Points of Mathematics Typing". – Henri Menke Apr 09 '14 at 08:06