It helps to remember that where the mind goes, energy flows. When we focus internally on various points in the body during posture practice, we channel fresh energy to that region. But when we plant our external focus on a single point ahead of us, we are attempting to improve our balance by zoning out ancillary thoughts. Concentrating on body parts that require greatest effort often helps us face our fears; while deep exhale helps us ease into postures more gracefully. It would help us to remember that, since each body is built differently, focus points may sometimes vary by ability. As a general rule of thumb, we would send our focus to that region of the body which needs our greatest attention.
Nevertheless, in ailment specific sequences, it is prudent to direct our attention to body parts that are impacted in specific ailments – i.e. knee joints for arthritis (of the knees), chest region for asthma, lower abdomen for constipation, upper abdominal region for diabetes, eyebrow center for hypertension, lower back for lumbago, pelvic region for piles (hemorrhoids), and back of upper thighs for sciatica.