Apart from having good grammar, you should also INTENTIONALLY plant these features in your writing plan/plot:

1) Connectors

2) Vivid descriptions of surroundings (sounds, sights, smells, touch/taste)

3) Expressions of feelings (through body language, facial expressions, dialogue/speech)

4) Inner Thoughts (internal struggle, worry, dilemma, question)

5) Actions and Reactions (to show interactions between characters)

Vivid descriptions of the surroundings as suggested by a student:

• Blazing past the other competitors like rocket

• The field was noisier than a wet market 

• Hearing cheers of encouragement punctuated the air

• The track was so hot you could cook an egg

• The spectators were chanting the names of their favorite teams fervently 

• The spectators held their breath as I gave a final push forwards, barely beating the last runner

Draft [focusing on describing surroundings and expression of feelings]

The sun was hanging high in the sky and the rubbery track was so hot you could cook an egg. You could hear cheers of encouragement punctuating the air as the runners did their stretches on the track. The noise faded away when the track marshall held up the starting pistol to signal the runners to get into their positions.

The red gun crackled and the racers were off! Harry had been lagging behind. Then unexpectedly, in the last stretch, he mustered all his strength and went blazing past the other competitors like a rocket. The field where the spectators were, was filled with excitement and fervent chanting of their favorite runners could be heard echoing across the field.

Harry was finally neck and neck with Tom – the fastest runner. The spectators held their breath as Harry gave a final push, barely beating Tom. Cheers roared out of the field as Harry took the first place.