What can I do to improve HDD health? which factors affect on HDD health? How long does a hard drive last? What is the optimum temperature for a HDD?
To answer your first question: In simple terms you cannot improve HDD health as it's a mechanical device with move parts etc. Yes there are tools but I can't see how it may improve if not extend the life if anything.
Second question: The condition of the drive, how it's treated i.e. dropped, bumped around etc. Heat is IMHO is the number one threat to any HDD.
Third question: There is no straight answer, any HDD can fail at any given time regardless of the age. Others can last decades.
Fourth question: Recommended manufacturers numbers - use google. The cooler the better but not too cold
Edit: Made some corrections to grammar and spelling.