To practise one-twos, you'll need at least two team-mates: a team-mate to pass the ball to and a defender.
The aim of a one-two is to make two quick passes between two team-mates when in an offensive situation, to break down the defence.
In our video, the two strikers are called A and B, which is simple and avoids confusion. When in possession of the ball, A makes a pass to B, who is close to him/her, and accelerates immediately in a forward direction. B passes back the ball straight away with one touch. Meanwhile, A has gotten rid of the defender by moving forward and is able to control the ball.
To succeed in your one-two and avoid losing the ball at every step of the exercise, you need to take into account three technical points: precision on the first pass, acceleration moving forward and orientation on the second pass.
We'll take things in order, and start with the precision of the first pass: in a one-two, your team-mate passes you the ball without control. So you need to make things easy for him/her by passing him/her the ball at ground level and on his/her strong foot.
Next, acceleration. Once you've made a carefully calculated pass to your team-mate, accelerate immediately in a forward direction to get in front of your team-mate. If you don't accelerate, you can't get rid of your opponent and you won't be able to receive the ball.
Lastly, the second pass: if you're playing the role of B in a one-two, you need to return the ball to A behind the defence. In other words, on the course of the player who's accelerating, thanks to the advice and inspiration of the previous paragraph. Rather than placing the ball at your team-mate's feet, place it a few metres forward to make things even more difficult for the defender.
Ideally, wait for the defender to come to you to intercept the ball before initiating a one-two. Once they're engaged in your direction, it'll be even harder for them to turn back and go the other way. If your opponent doesn't come spontaneously towards you, head in their direction to force them to take action.