Midrash Genesis Rabbah:
Rabbi Levi explains that when Abram was traveling through various lands, he was people going to drunken parties. "May I not be a part of this country!" he would say. But, when he reached the location of Tyre, near the Land of Israel, and saw people working at weeding and hoeing in the proper seasons, he said: "may my portion be in this country."
(As told by R. Harvey J. Fields, A Torah Commentary for Our Times, p. 39)

Midrash ha-Gadol (12:12):
It was not a lie for Abram to call Sarai his "sister" since Sarai was his niece, and relatives may be termed brother and sister.
Rashi asserts that the term "daughter" can also be used regarding a granddaughter, and thus "sister" can be used regarding a niece.

Faced with the fear that he might be killed by the Egyptians, Abram may have decided to tell a "half-truth." He would say that Sarai was his "sister", which, in fact, she was, but he would not reveal that she was his wife. The commentator Nachmanides condemns Abram for his behaviour. He says that Abram "committed a great sin" by not telling the truth about his wife. "He should have trusted that God would save him and his wife and all his belongings. . . "
Other commentators disagree. Rabbi Samson Raphael Hirsch . . .argued that Abram's actions were honourable. He knew that they Egyptians would not deal harshly with an unmarried woman travelling with her brother but that they would kill the husband of a beautiful woman and rape her. So he acted to protect both Sarai and himself. . .
The issue remains unresolved. Was Abram justified in lying? Is using a half-truth lying? and what about Sarai? Was it her responsibility to tell the truth rather than follow Abram's instructions?
(R. Harvey J. Fields, ibid)

The Talmud (Sanhedrin 69b) identifies Sarai with Iscah, daughter of Abraham's deceased brother Haran, so that in this Sarah turns out to be the niece of Abraham and the sister of Lot and Milcah.

. . .The deception leads to an improvement in (Abram's) status, but the deception is uncovered and they are summarily dismissed. They depart, however, with their newly acquired goods intact. The tale portrays Pharaoh as a dupe and eals with the "us-them" theme in a humorous and thoroughly traditional way.
This passage is not a tale about unethical behaviour, but a story of marginalised persons who succeed in roundabout, unorthodox ways. . .
- The Torah: A Women's Commentary, p. 63

R. Kenneth J. Weiss:
Vayaavor Avram, "Abram passed through" (Gen. 12:6)
My parents have just moved into a full-care senior residence. Life - even in later stages - requires transitioning from one experience / place / situation to a new and (often radically) different one.
Abram experienced this. "God forth, " he is told: separate yourself from all you know; go "to a place that I will show you" (Gen. 12:1). So, at seventy-five, Abram departed the homeland of his youth for "a place he did not know."
Abram grew to know what my parents continue to learn: so long as we live, transition is a constant
One Hebrew root ע-ב-ר captures this concept. Since one of Abram's ancestors is Eber (עבר), perhaps successful transition between life's stages was built into Abram's gene code.
Presenting Abram, our paradigm. Know that, for us as for him, life requires episodic, and often difficult, trasitions. Abram didn't just move physically: he transitioned from one of his life stages to the next - and di so with grace and conviction.

Abram's the best. Perhaps that's why he's called אברם העברי (Avram HaIvri): Abram the Transitioner (Gen. 14:3)
(From Voices of Torah, p. 32)