Like life, you can do everything right, but if you aren’t aligned to the correct target, you’ll be looking in the wrong place to correct your inaccuracy, perhaps messing up a perfectly good swing. Generally I am most concerned with shoulder alignment, and less with hips and feet.
An easy and sure way to check your alignment is to lay an alignment stick on the ground, pointing on your target line. Either near the ball or your toes, it does not matter. What you’re going to do is set up to the ball preparing to swing, and at the last second before your takeaway, FREEZE! Keep your body perfectly still and do not look at the target. Simply, and carefully so as not to move any part of your body other than your arms, lift the club to pin it against your sternum, parallel to the ground. Without moving your head, you should easily be able to see if the club against your sternum is parallel to the alignment stick. When practicing, I hit two balls doing this, one without, and repeat. Even when I am playing well–it helps keep the eyes and instinct trained. Alignment errors tend to creep in gradually, so it pays to not become complacent.