Forecasting sales (the top line) is key to forecasting what the result of the business (the bottom line) is going to be.
There are two elements to this - the science and the art!
Most companies focus on the science - they analyse what has happened in the past (actual - trends) and project forward to generate a forecast - hopefully they’ve got some assumptions to justify any significant changes.
The forecast can be made more robust by considering what is or might be happening in the market place (market intelligence). As well as being close to the market, there is an art to this. It’s essential that there are assumptions that you can check back to during the year.
Of course your forecast will be supported by a tactical plan which you follow!