A Halocha A Day

Meals on Erev Shabbos:

We may eat and drink until Shabbos begins. Once Shabbos has began we are obligated to make Kiddish before eating.

Our Sages forbid eating lavish meals Erev Shabbos. The reason is because we want to show honor to Shabbos and therefore enter with an appetite, we eat larger meals on Shabbos and also the Sages were worried someone might be too engrossed into their eating and will not be able to prepare accordingly for Shabbos.

We may partake in a Seudas Mitzva on Erev Shabbos. Its best to have such a meal in the morning.

Adding to Shabbos:

Its is a Mitzva to add onto Shabbos. The custom is to accept Shabbos slightly earlier on a Friday and wait a little later on Moztei Shabbos before concluding Shabbos.
The amount of time needed for this "addition to Shabbos" is not given in the Gemora. The general custom is 20 mins before sunset to accept Shabbos.
One should state verbally that they are accepting this addition to Shabbos by saying, "I hereby accept tosefes Shabbos."