Aristotle said that ethos consists of three sub parts: (1) good moral character, (2) good sense, (3) good will. If the writer or speaker can project an image of good moral character, then the audience will think that he or she can be trusted because the person has a conscience that will keep him or her on the up and up. Good moral character is projected by avoiding statements that could cause people to suspect that you would do something unethical and sometimes by making clear statements of concern about moral or social issues (being careful not to take stands on hot issues that might alienate the audience).
If the writer projects an image of one who has good sense, then the audience trusts the judgments made by the writer. Good sense is projected by adhering to sound reasoning and by supplying apt examples or parallels. Common sense is largely the art of seeing how things apply in more than one context, and that is shown by citing for instances, or examples.
Good will is the attitude of the writer or speaker toward the audience. If the writer is suspicious of the audience or if he is trying to deceive them in some way, the audience picks that up as a sense of ill will. On the other hand, if the writer has the best interests of the audience in mind and has nothing (or nothing significant) to gain by the suggestion being made, then the audience senses that the writer is on their side. One projects good will by explaining the benefits of an idea or suggestion to the audience and sometime by complimenting the audience.
Just as you would use these methods to create a strong ethos, so you would look for these techniques when you are trying to discover the ethos in a text. Ultimately, a good ethos is one that creates trust, and that usually comes when the writer or speaker succeeds in showing the audience that he or she is part of their community and shares their goals and values.