This policy note by Ha-Joon Chang is from 2007 and hence does not include reference to the most recent discussions, but it is still well worth reading as an introduction: http://esa.un.org/techcoop/documents/PN_SOEReformNote.pdf
In addition, it it's worth noting that privatizations potentially have major effects on issues such as transparency, accountability, representativeness etc. These things are often difficult to price but important for the functioning and limits of democracy.
In addittion to the former, another criteria to consider is: When the prices charged by the private sector are abusive, in which case state intervention (for at least 30% of the market volume) is necessary.
The state owned enterprises may be privatized when they are are continuously running in loss for more than six years due to inefficient administration, mismanagement, malpractices, unnecessary rise in cost including wages, uncontrolled higher maintenance cost and inability of government to run or modernize. Disinvestment policy of Indian government is a reference.