Etiquette and guidelines for sending pre-published work to other people?
1) Talk to your advisor. She or he should be aware of your intention to send your work to a third party, and can even suggest you the right persons to send your work to.

2) Usually you can ask only people you know personally (or your advisor knows personally).

3) In our university internal review of two colleagues is required if you want to publish a technical report. So, sometimes showing your manuscript to somebody else is required.

4) You might like to stress that the manuscript you are sending is still a preliminary version, and ask the reviewer to keep confidentiality issues in mind.