Familiarity should increase consideration, not reduce it.

Comfort tends to erode manners. The people we know best are the ones we cancel on, interrupt, answer distractedly, and take the least trouble with, on the assumption that the relationship can absorb it. It usually can, up to a point, and the accumulation is felt long before it is mentioned. Closeness should be a reason for more care rather than less.

Pick the person you are most casual with and give them the courtesy you would give a new acquaintance for a week. Reply properly, arrive on time, listen without reaching for your phone. The change registers faster than you would think.