How to thank someone who proofread my scientific paper?
The author would like to thank [colleague name and title] for constructive criticism of the manuscript.
No need to get into additional details as after all you are thanking your colleague.
First, I disagree with the answer(s) suggesting the proof-reader be acknowledged generally for contribution to the paper, since that gives the false impression that they contributed scientifically. That would be a misrepresentation of the facts, and also puts some limited responsibility on them for the contents of the paper if not beyond that.
For "mere" proof-reading - it's a question of the degree of contribution. In a typical case of finding typos and a few comments about style, I would buy that person lunch, not put them on the paper. But if my English was weak and the proofreading contribution is significant, then yes, by all means, that person can be acknowledged - for proofreading (but ask them first if they want to be mentioned).
If it's a thesis or a book I'd be more lenient with acknowledgements, even for a little proofreading help; and doing so is pretty common.
I would like to thank @InkBlot for his constructive criticism on the manuscript of this post.
Yes, it is common, fair and sometimes compulsory to acknowledge your funding agency and everyone who somehow contributed but does not qualify as an author, such as the case you mention (proofreading).
Check the journal/conference you are submitting to and stick to the same format. Most articles have a final (unnumbered) section called Acknowledgments just before the References. If not, you are free to add it.
The best acknowledgment is simple, straightforward, and honest.
In the case of proofreading, it is common to write: "Thanks to John Smith for proofreading the article". Everyone in the domain knows what proofreading means, so there is no need to be creative or misleading about it.
More tips here: http://www.aje.com/en/arc/editing-tip-writing-acknowledgments/