Guideline: Don’t start a sentence, clause, or phrase with there is/was/are/were.
1. There and is are words that have no specific meaning in and of themselves (specifically is is a light verb, and were such a distinction to be made, there would be a light subject).
2. Subject and verb positions are two of the most powerful positions in the sentence. Why would you put two words with no intrinsic meaning into those positions?
3. Reading is easier to parse and retain when the subject of the sentence is a clear agent (the person/thing doing the action of the sentence) and the verb contains intrinsic information about the action of the sentence (i.e., is not a light verb).
4. Writing a sentence correctly gets to the point from the first word. There is delays meaning and burdens the end of the sentence with more complicated sentence structure to make up for the fact that the information contained within cannot make use of the subject and verb positions.
For more specific explanations and example and where exceptions may be appropriate, visit the original article.