With that in mind, Chris Cameron of the African-American Intellectual History blog has provided some useful advice. Here is a small taste:
In terms of who should write for you, it is fine to have a letter from your doctoral advisor as long as her or his expertise also covers the topic of your new project. You should have full professors or people very well known in their fields writing for you, and both of your letters should not be from people too close to you. So if your advisor is writing, don’t have someone else from your dissertation committee or a colleague at your own institution write you a letter. You also want to avoid letters from your grad school friends, unless that friend has gone on to be a full professor, endowed chair, or someone very well-known and respected in their field. If they are still a junior faculty member or recently tenured, ask someone else.
Read the entire post here.