How to make a decision based on Buddhist principles?

Samma Ajiva - the third and the last member of the morality group of the Noble Eightfold Path is what you want to read about. The Right Livelihood means abstaining from any of the forbidden modes of living. Five kinds of livelihood are discouraged : trading in animals for slaughter, dealing in weapons, dealing in slaves, dealing in poison and dealing in intoxicants. So select a job which doesn't require you to do those.

Which college to go to? If you are looking for additional criteria apart from academic facilities, select a college where Buddhism and Vipassana meditation is taught. Select a place where you have a high chance of meeting "Kalyana Mittas". In other words, a place where you can make friends with people who learn and practice the Dhamma.

To me, this is not really how Buddhism works. I think of it this way:

Meditation practice can help you to have clarity (among other things). Tonglen can help you to find compassion. And other practices can help with find other things. All those things may be useful to you when making a decision.

But generally, aside from some very specific items, Buddhism doesn't care which choice you make. Buddhism doesn't know anything about what college is best. Your practice might help you to recognize that certain choices might have unskillful outcomes, but I don't suspect you'll have much luck looking to Buddhism for specific decisions about non-Buddhist related topics.

That said, Buddhism CAN help you to be present and mindful while you use other means to decide.

:)

In the context to buddhism, it would discourage worldly pursuits. Things like college, ambitions and future plans all lead to becoming, becoming leading to rebirth. You are generating more Karma by following these pursuits. I think the question would be more "Why has 20 years of practicing meditation and buddhism not lead me to the path?" :-).

A book by Bhikkhu Basnagoda Rahula, Ph.D entitled The Buddha's Teachings on Prosperity At Home, At Work, and in the World devotes a chapter to "The Buddha's View on Decision Making".

I have seen no other cause than the presence of false views to block the origination of right thoughts in the mind and to corrupt the right thoughts already present in the mind. I have seen no other cause than the presence of correct view to inspire the right thoughts already present in the mind. ~ The Buddha, The Numerical Discourses

Venerable Dr. Rahula, outlines 10 kinds of fallacies in reasoning (from several suttas including the Kalama, Bhaddiya, Canki and others) that if one were to believe to be true could create such false view.

Fallacy 1. Reported information is true
Fallacy 2. Traditional values, beliefs, and practices are actual truths
Fallacy 3. Social truths are actual truths
Fallacy 4. The texts are true
Fallacy 5. Logical reasoning is always correct
Fallacy 6. Reasoning based on imagination and speculation is correct
Fallacy 7. Hypothesized reasoning is correct
Fallacy 8. One should accept a view because it is compatible with one's own way of thinking.
Fallacy 9. One's persuasive skill validates the message
Fallacy 10. Individual authority is a dependable criterion for making decisions

Each of the fallacies is explained in detail and the following chapter details "Correct Reasoning, Right Decisions".

If you understand that this action is right, harmless, blissful, beneficial, and admirable, take that action and follow it. ~ The Buddha, The Numerical Discourses

The four forms of correct evaluation (from the Kalama Sutta) are:

Right Evaluation 1. Wrong motivations lead to wrong decisions
Right Evaluation 2. Absence of wrong motivation leads to right decisions
Right Evaluation 3. Consequences of a decision make it right or wrong
Right Evaluation 4. Attention to the views of qualified people lead to right decisions.

In summary, the Buddha spoke of the correct way to make decisions on many occasions. Due to the way discourses are categorized, it's not easy for the average person to pick out the teachings of the Buddha on such practical matters in any sort of an easy way. This book has done that and combines an easy to read style with the expected references to the suttas from which the information is taken. It's available from Wisdom Publications if you are interested in reading it in full.