What can cause GDP increase in the short run?
Increase in overall jobs, more specifically in the labor area. Seeing as how we live in a capitalist society, the higher-ups in businesses like to hire low-wage workers to make an increase in profit. This, in turn, causes these corporations to (usually) have lower prices on goods, which then has more people buying and selling in the national and international economy. So, in the end, it all starts and ends with "glorious" capitalism.