I'm a big supporter of walking into headstand rather than jumping into it. This not only prevents you from kicking too hard and falling over, but it also strengthens your core. Flexible hamstrings are key to walking into headstand, so start with this Wide-Legged Forward Bend. This pose will also open your shoulders.
Stand with three to four feet between your feet. Turn your toes in slightly and interlace your fingers in a double fist behind your back. Inhale to engage your abs and pull your hands away from your shoulders. Exhale to fold at your hips, keeping your legs and spine straight. Hold for five deep breaths, trying to lower your hands toward the floor.