Don't strengthen a tight muscle. The PDF must include inhibitory techniques:
: Imagine a straight line running through your ear, shoulder, hip, knee, and ankle .
If you are looking for immediate ways to address posture, MedlinePlus and Better Health Channel suggest these basics:
Keep your head level, shoulders back, and stomach pulled in.
Most posture guides waste 30 pages on anatomy. This PDF covers the basics—upper cross vs. lower cross syndrome—in about 5 pages and moves on. You’ll learn why your pectoralis minor is pulling your shoulders forward and why your glutes have fallen asleep. No medical degree required.