Nowadays most economists use myopic first-differencing to make their-seat-of-the-pants forecasts: predict the growth rate of most flow variables (e.g. GDP, etc.) will continue. It's not a bad way to make rough predictions. But if it works, what does that say about rational expectations??
Another way that many (most?) business economists make their forecasts, though, is at least as interesting. A business economist shared this technique with me several years ago:
Subscribe to at least 20 forecasting services and take an average.
Back in the day when I used to do forecasting, I used a big simultaneous equation SAS model to generate my forecasts for GDP, personal income, etc. for the US and for personal income, employment, etc. for Missouri, Kansas City, and St. Louis. The growth rates for the National Income Product Accounts often would turn up to be some ridiculous number. So I compared what I had to what the Blue Chip Economic Indicator folks (a survey of forecasters) said and I made some adjustments to my national forecasts based on the average "Chipper" growth rates.
Now I prefer the Magic 8 ball and a dart board.