In what order should I write acknowledgments?
It generally doesn't matter much (though I wouldn't suggest using in increasing order of helpfulness), but if some people deserve special thanks they should be singled out.  I'll often write acknowledgements in this sort of format:


I thank Prof A for encouraging me to think about this problem and Prof B for the realization that it could be approached by X ("chronological order").
I also thank C, D and E (alphabetical order) for useful discussions and feedback.
This work was partially supported by Grant 12345.


If it's a co-authored paper you can separate sentences/phrases for specific thanks from each author.  

Generally my advice on questions like this is just to look at a bunch of other papers, see what they do, and learn from that.