How to state should and must, the verb deber.
I have read several threads on this, and there still seems to be disagreement / and some ambiguity. According to the dictionary, and some other postings at SpanishDict.com,,,
"Tú debes comer". Literally means "You must eat". Present Indicative.
"Tú deberías comer". Literally means "You should eat". Conditional Indicative.
It seems "debes" represents a stronger obligation, and deberías, a more polite, less imperative statement or request.
To me, it appears that the following supports that idea.
"Yo debería hacerlo", I should do it."
"Yo debo hacerlo", I must do it."
But, a common translation, and several posts here translate (although some disagree)
"I should do it" is "Yo debo hacerlo". 
I am still not sure how to state the difference between having to do something, "must", and the less obligatory, "should".
For example: How would you translate? "A man's feet must be planted in his country, but his eyes should survey the world" . ---George Santayana---
I would appreciate it, if you could help me understand. Me duele la cabeza! 
Thank you!
2 Answers
Forget about the exact translations.
"Tú debes comer" sounds fine if you are going to say something like "You should eat... while someone else should drink"; otherwise, you don't say "tú". "Debes comer" sounds a bit unusual, almost as if it was your responsibility to do so.
"Deberías comer" (without that confusing "tú") is considering what might be best for you, more polite.
"Debería hacerlo" is considering something as a likely best option.
"Debo hacerlo" sounds as it is your duty to carry out some task.
Debes comer is what you say to an anorexic person.
Deberías comer is what you say to a drunk person.
