Regarding the Nativity Fast

For those interested in going old-school, here's an excerpt from the so-called Small Home Rule, which is a compilation from various books for lay people on things related to praying and fasting.

From the Great Rule. From the day of holy apostle Phillip until the day of our holy father Nicholas one is to eat raw food on Monday, Wednesday and Friday. On Tuesdays and Thursdays as well as on Saturdays and Sundays one can eat fish. From the day of our holy father Nicholas until Christmas, we eat fish on Saturdays and Sundays, while on Tuesdays and Thursdays we consume cooked food with oil and we also drink wine.

From the Nomocanon. Before Christmas fish is allowed during  the fasting period only on Saturday and Sunday, while on Tuesday and Thursday oil and wine is allowed. On Monday, Wednesday and Friday we fast until the 9th hour (i.e. 3pm). If someone cannot drink water on Monday, oil and wine is allowed. Wednesdays and Fridays should be observed as strict as one's strength allows, save for great and burdonsome ailment.

From the Rule of Solovetsky Monastery. During the Christmas fast until the day of Saint Nicholas the Wonderworker, one is to eat fish on Saturdays and Sundays, on Tuesdays and Thursdays. On Saturday and Sunday - twice*, on Tuesday and Thursday - once during the day. On Monday shchi (simple cabbage soup) is eaten with one cold dish and one hot one. On Wednesday and Friday shchi is to be eaten along with two cold dishes. From the day of Saint Nicholas until the Christmas Eve we eat Plasti (dish with cold fish), on Monday, Wednesday and Friday we add two cold dishes to Shchi; on Tuesday and Saturday we add one cold dish and one hot dish to Shchi. On Christmas Eve on Saturday and Sunday we eat with oil twice a day; on other days we eat as during the Great Lent.

*Fasting also includes the number of dishes eaten. Unless specified otherwise - it is assumed that one eats twice a day, either after the 6th (12pm) or the 9th hour and then after the Vespers (the choice will depend on the way services are conducted). Breakfast is considered a sort of vanity and ideally people are to pray in the morning instead of eating.