To fix run-on sentences, you need to ensure that each independent clause is correctly separated, either by punctuation or conjunctions. Here are the corrected versions of the sentences:
The movement of the team was helpful. The players were excited.
Corrected : The movement of the team was helpful; the players were excited.
Be careful not to spill the milk. It will ruin your new dress.
Corrected : Be careful not to spill the milk; it will ruin your new dress.
I wanted to solve the mystery. It had been baffling me for many months.
Corrected : I wanted to solve the mystery because it had been baffling me for many months.
We are in danger of failing. We must work harder on our school work.
Corrected : We are in danger of failing, so we must work harder on our school work.
Can I go to the cabin in the woods? I love to fish at the lake.
Corrected : Can I go to the cabin in the woods? I love to fish at the lake.
Through my experience, I have learned a lot. I have learned to be disciplined.
Corrected : Through my experience, I have learned a lot, and I have learned to be disciplined.
To correct run-on sentences, you can use a period, a semicolon, or a comma with a conjunction depending on the connection between the clauses. Choose the most appropriate method based on how closely related the ideas are.