Red-flanked Bluetails typically inhabit dense undergrowth in coniferous, mixed, or broadleaf forests, preferring areas with mossy ground, fallen logs, and near clearings or water bodies. During migration, they can be found in a wider variety of wooded habitats, including parks and gardens, particularly where there is dense cover. They breed across the taiga and boreal forests of northern Eurasia and into mountainous regions of East Asia.

This bird is often shy and elusive, preferring to stay hidden low in dense vegetation, making visual sightings challenging. However, its presence is frequently betrayed by its beautiful, high-pitched, and warbling song, which includes trills and flute-like notes, especially in the breeding season. Its call is a soft, distinctive 'tac' or 'chick' sound. Patience is key; look for subtle movements in the undergrowth or listen for its unique vocalizations.

Red-flanked Bluetails are most active during the early morning and late afternoon hours. They are long-distance migrants; therefore, observing them depends on the season and geographic location. During the breeding season (summer), they are found in their northern territories. They become more widespread and potentially easier to spot in passage habitats during spring and autumn migration periods as they move between breeding grounds and their wintering areas in Southeast Asia.