Holt's method (see: otexts.com)
Holt (1957) extended simple exponential smoothing to allow the forecasting of data with a trend.
This method involves a forecast equation and two smoothing equations (one for the level and one for the trend):
Forecast equation: ŷ = l + h * b
Level equation: l = alpha * y + (1 - alpha) * (l + b )