While playing as a striker, make sure that you hold your line whenever the ball is being played in the midfield. Always ask for the ball when you think you are not offside. How will you know that you are not offside? You will simply check whether all parts of your body are either in line with the defender or behind him. The defender faces the midfield while you are facing towards the goal, so the best way to make sure that you are in line with the defender is by keeping a check on his forehead. You should always be able to see his forehead whenever you ask for the ball. This way, you know that your eyes are behind the defender, which makes the rest of your body behind him too.
As soon as you are sure that you are onside, ask for the ball. Don’t scream as the referee will give you a yellow card, simply extend your arm forward. However, make sure that you run before you extend your arm. This will help you because if you are not running, that means that reaching the ball before the defender will be impossible for you.
Once you know that you are in line and the ball has been played, run towards the ball. If you have kept your line in check then there is no way that you are in an offside position. Reach the ball before the defender, run towards the goal and try to score.