What is the best way to avoid the personal issues in your office?

Keep your private life private, use discretion when talking to co-workers about your family and life outside of work, and stop people politely when they start to talk about others and share too much information. They will understand that you are not a gossip and find someone who enjoys it.

stick your mind on work, like a horse which is in a race, the only way he sees is what in front, not the sides because sides are covered by eye-covers, he can't see any side

Easily avoid by to keep maintain healthy & professional environment in your office. You should never give your consentrate & disclose your personal matters in non healthy activities.

Simply by keeping active professional ethics and also maintain them at work place.

Serious work ... (Red lines)

with communication 

Team work is the best solution.

When everyone work like a team with greeting each other than there is no way out for issues.

Make the staff engaged at work. Give training on Best Work Environment.  Explain about the people behaviour to be at work. Call the staff and warn, to not repeat to bring the personal issues to the office.