Just little things can make a big difference in how your sentences sound to a reader.  Here are just a few notes:

• Try not to use the same noun twice in one sentence.  I.E. “The ground felt hard and cold against her palms as she hit the ground.”  Also try not to use the same verb or adjective.
• Make sure things in your sentence don’t rhyme.  “The long hours of study put quite a strain on her brain.”
• Vary your sentence structure a bit.  Move the ‘he said’ around.  Take it out.  Attach an action to the end of it.

‘He shrugged.  “I thought you’d like to know.”

‘”Well, I don’t want to know,” he snapped.

‘”There’s no need to get angry.”

‘”I just want you to leave me alone,” he said, turning his back on his friend.’

So, you can put things in front or behind the spoken part, put or leave off a ‘said’ and then attach an action to it.  Mixing up what kind you put there will help keep your sentences from dropping into a monotony.