Bringing in Shabbos Early

What are the clalim for bringing in early Shabos.
When sould one daven Mincha and Maariv.

Answer:

The common manner of bringing in Shabbos early is by davening Maariv before nightfall.

If a person wishes to do this, he must ensure that he davens Minchah before the time of pelag ha-minchah, which is one and a quater hours (sha’os zemanios) before the end of the day, or one and a quater hourse after minchah ketanah (which is nine and a half hours into the day). This follows the opinion of Rabbi Yehudah, who permits davening Maariv early, but insists that one must daven Minchah before pelag ha-minchah.

An alternative method for bringing in Shabbos early is to make Kiddush early. This can be done anytime after pelag ha-minchah, and some prefer this method, which allows Maariv to be davened later, after nightfall. Of course, the Minchah prayer must be davened before one makes kiddush.

Although this latter method emerges from the writings of Rishonim, the Vilna Gaon (in ma’aseh rav) appears to reject the option of making Kiddush before Maariv.