If you don't train hard, you won't succeed in sport.

You succeed in sport you hard.

If you train regularly, you can improve your performance.

You improve your performance you regularly

Take a spare pair of running shoes, because it's possible that you will need them.
a spare pair of running shoes you them.

We’ll go for a picnic by the river tomorrow if it doesn’t rain.

it , go for a picnic by the river tomorrow.

If you enjoy your sport, it doesn't really matter whether you succeed or not.

It really matter whether you succeed or not you your sport.

Take a waterproof coat with you because It's possible that It will rain.
a waterproof coat with you it

If you don't eat and sleep properly you won't develop as an athlete.

You develop as an athlete you properly.

Take a first-aid kit because it's possible that someone will get injured.
a first-aid kit someone injured.