Make sure the facts as stated in the document are correct, helpful, and on topic.
To do a technical accuracy review, you really need to know your subject matter, probably as well or better than the original author. Use whatever other documentation is available for your subject, including man pages, program documentation, other printed books, etc. You might also use mailing lists on the topic, asking for third parties to verify certain facts of which you are in doubt.
When doing this type of review, consider if the information is only valid for certain types of hardware or software. If this is the case, make sure to note the limitations of the document within the document, either within the abstract or as a note at the beginning of the document. For example, if the solutions in the document only are relevant for one type or brand of hardware, make sure that that limitation is defined. This will keep readers from trying to apply a certain type of technology to an application or situation where it will not work.
The same should apply for the prerequisite knowledge of the reader. If prior knowledge of a subject is assumed or required, the author should say so somewhere at the beginning of the document, and it's helpful to ask that authors provide a Resource section for further reading, to bring readers that much closer to the required information.