Begin by making sure you have no trouble doing regular pushups, and can perform as many as you like with complete ease and in perfect form. It will serve you best if you learn to do perfect two-arm pushups first, focusing on quality as opposed to quantity. Place your arms shoulder-width apart, and keep your back straight as you lower yourself – then pause, and push back up quickly. Try doing 10 to 15 perfect two-arm pushups daily, and once you have these down pat, you are ready to begin working on the one-arm variant.
Next, slowly start moving towards the one-handed pushup. First, introduce some changes in your regular pushup – for example, you can try a more asymmetrical stance, in which you can place one arm close to your chest, and the other near your abdomen, as you do your pushups. This will put more weight on one arm, and less weight on the other, thus preparing you. Switch the positions of arms, and keep practising these until you can do them with complete ease.
Now, you are ready to attempt the one-handed pushup – the first time around, don’t focus on getting it absolutely right, and just try it out in order to ease your body into it. Get down on the floor, on your hands and toes, and plant your feet wide apart. Then, with both hands on the ground, lift your body up, making sure it forms a straight line, and does not sag at any point, particularly near your back.
Maintain this position, and slowly lift one arm off the floor and rest it behind you, on the small of your back. Take some time to get used to this position, with just one arm supporting your body weight. Then, slowly bend that one arm at the elbow, and lower yourself, bringing your chest to the ground. Go as low as you can, then bring yourself back up, straightening your arm, and making sure, once again, that your body stays in a straight line throughout.
Try a couple more, doing a few everyday, until you get used to it. Then, you can begin to incorporate the one-handed pushup into your daily exercise routine. Do half the pushups with one arm, then switch and do the rest with the other arm, to make it an even workout.