There’s a great article at the US News and World Report website titled Can Facebook Posts Lead to College Rejections? The bottom line is what you would expect: if you post something reckless, you get a reckless reputation. So use your good sense, assuming you have any. And for a guideline, check out the article.
The lesson here, however, applies to all areas of life – not just college admissions. Consider the advice as applying to all aspects of your life, professional or otherwise.