Toss the ball the front and try to hit it in front of yourself.
Toss the ball the front ボールを前にトス、投げる
try to hit it in front of yourself 自分よりも前で打つように心がけて
If you toss it to your side, it would become a slice serve.
トスを横にあげるとスライスサーブになってしまう
If you want to serve a flat-serve, toss it to the front.
フラットサーブを打ちたければ、前にトスしてください。
Toss the ball to your front and aim to contact it while it's directly in front of your body.
もうとても良い説明を貰いましたが少し訂正しても宜しいでしょうか。
Toss the ball the front => Toss the ball to your front
and try to hit it in front of yourself => and try to hit it in front of you.
又は and aim to contact it while it is directly in front of your body.
If you toss it to your side, it would become a slice serve. =>
If you toss it to your side, it'll (=>it will) become a slice serve.
If you tossed it to your side, it would become a slice serve.
(これでより正しい時制の組み合わせとなります。)
失礼いたしました!