Answer:
The key to keeping an open mind is to go in truly blind to the trial. That means the potential juror shouldn't have any exposure to media about the defendant or the events in question. The juror should learn everything during the court case itself when the prosecution presents the case carefully laid out, and the juror should also weigh the defense argument as well. This is why jurors are not allowed to consume outside media, especially news articles, or watch news on tv. In some cases, jurors are sequestered to isolate them further from the outside world to prevent accidental jury tampering. Unfortunately, a lot of news in the modern era tends to have an editorialized spin to it. Meaning there are opinions, conjecture and speculation injected into things when they shouldn't be there. It should be facts only.
In addition to going into the case blind, the juror should also be free of any prejudices about the person's class, race, etc. These preconcieved notions tend to potentially affect the decision a juror would make, and these notions tend to be unintentional. If the juror could spot these tendencies and try to eradicate them (before they get worse), then it likely would lead to a more impartial juror.
Here are 3 things you could do to adhere to the philosophy of "innocent before proven guilty"
Keep the idea in your head that another person could be guilty.
Try to put yourself in the shoes of the defendant.
Everyone is human. Even if the first impression may have been a bad one, it could have just been a bad day for the defendant. The same may apply to the day in question involving the crime.
At the end of the day, keep in mind the most important thing: The burden of proof lies with the prosecution and not the defense. It's up to the state to prove the defendant guilty. This is why the verdict is a simple binary choice of "guilty" vs "not guilty". It's because the jury is testing the claims made by the prosecution.