The First Mitzvah when Shabbos is ushered in is the kindling of the Shabbos lights.
The Ohr Hachayim explains: Hashem created the world to last 6 days, and every Shabbos the world receives an injection of renewed creative strength to last for another 6 days. At Creation, the first thing that was brought into being was light. Therefore, the first mitzvah at the arrival of Shabbos is the kindling of the lights, to correspond with the light that was the first creation. ~ Tzemach Dovid as quoted by R’ Dovid Meisels