The new growth on evergreens is referred to as "candles" because of the candle-like shape of the branch tips. Cutting the candles back halfway, before the needles unfold, will keep the tree more compact.
Candling should occur between late March and mid-May, depending on the area and the weather.
Don't try to prune once the needles have opened fully or you may end up with a misshapen plant, since these trees cannot replace their growing tips.

