Tax cuts historically stimulate the economy, for obvious reasons. It increases the probability for consumer spending.
Low deficits also tend to help, and low interest rates as well (balanced to the competing inflationary trends).
But yea, Presidents more or less don't affect the economy that much. Much of it has to do with cycles and external stimulation.
The most important thing they can do is to try to mantain stable conditions both domestically and abroad.
