Note that most conifers can be used here: spruce, fir, pine, redwood. Flavor is very variable from tree to tree and species to species. Be very careful not to pick from the yew, which is a common landscaping plant in the US. It is highly toxic.
Bring the sugar and water to a boil in a lidded pot, stirring to make sure all the sugar is absorbed.
When it hits a boil, turn off the heat. Stir in the spruce tips, cover the pot and leave to cool. The longer you steep the syrup, the stronger spruce flavor you'll get. I let it steep overnight.
Strain the syrup through cheesecloth, add lemon juice (if using) to taste and bottle.