Most of French customs centre on religious events or major dates in the calendar.
On December the 6th in the northern parts of France they still celebrate St Nicolas , a day when children receive goodies in their shoes. This is what has now been adopted as Santa Claus or Father Christmas in other countries on the 25th.
Naughty children find a piece of coal in their shoe instead of treats and at one time they even found a 'martinet', a mini cat of night tails, left by St Nic's companion, Père Fouéttard. One of my brothers was given one, swore vengeance on St Nicolas, and cut all the leather straps off to make sure this was not used to punish him at a later date!
Christmas is a big event but far less commercial than in English speaking countries: Many people have a Christmas tree and a crib as seasonal decorations. The cribs are particularly interesting as they have many additional characters called Santons, made in Provence, which range from the kings' retinue to simple figurines representing a dairy maid, a poacher, a fish seller, a mayor etc...These are usually set out on Christmas eve and are often kept throughout January unlike in Anglo-saxon countries where it is considered bad luck to keep Christmas decorations longer than 12th night.
On Christmas eve many people go to midnight mass and afterwards some have a midnight meal called Réveillon and open some presents. On Christmas day numerous relatives gather for a family meal which often consists of an oyster starter, then turkey stuffed with chestnuts with side vegetables and ends with a Yule log cake. Other traditional foods at that time is boudin blanc, a saucage made with white meat, and foie gras.
Incidentally it is not a French tradition to send Christmas cards. In France wishes are sent for the New Year , they can be on plain cards, and be posted any time in January.
New Year's eve is really big with many parties, champagne drinking, and people coming out of their houses and wishing neighbours a happy New Year at midnight and dancing into the early hours. In larger towns there are big fireworks.
The 6th of January is Epiphany, which is supposed to be the day that the three kings arrived at Bethlehem and on that day people serve a large cake made out of golden puff pastry and filled with marzipan called Galette. In it is hidden a small china figure usually in the shape of a baby and the person who finds it in their portion becomes "king" or "queen" for the evening and can order people to do various things which make everyone laugh.
Pancakes are made on Shrove Tuesday, the last day before Lent. These are wafer thin and quite large and get stuffed with various things savoury or sweet.The original idea was that people used their reserves of fat and flour before the forty days period of Lent before Easter when they fasted .
During Lent the church bells are not rung till Easter morning. Hens' eggs are decorated and hidden for children to go on an egg hunt in the morning. They also are given chocolate bunnies and tiny chocolate eggs.The bells are supposed to have dropped them "on their way back from Rome" but in other regions it is supposed to be te Easter rabbit. In some towns there is a carnival half way through Lent, with children dressing up in funny costumes.
On April the first children make little paper fish which they try to stick or pin on other people, and it is a traditional day for playing pranks on other people and send them on pointless errands. The media also take advantage of this and make up plausible but rather ludicrous stories.This is known as "Poisson d'avril".
On the first of May it is a tradition to present other people with sprigs of Lily of the Valley for good luck.
In the Summer there are various processions to celebrate the local saint or the feast of Our Lady, and in Brittany these are called "Pardons", an occasion when the women pull out their traditional costumes and lace hats, which are superb, for these celebrations.
The 14th of July is France's national day. It is the anniverssary of the storming of the Bastille, a fearful prison in Paris, by the populace in 1789. It was the start of the french revolution. It is an official holiday. There is a big military parade in Paris and in other towns dancing in the town squares and great fireworks are held all over France.
Halloween has now been introduced in recent years but is only a children's thing and insigificant compared to the event in the USA. What the French do on the first of November is go to visit their family graves with pots of chrysantemums, no matter how cold, wet or windy it is (which it always seems to be!).
There are various military parades all over France on Armistice Day and flowers are put at the grave of the unknown soldier under the Arc de Triomphe in Paris.
Weddings, christenings and communions are big events when all the family gathers together. The French are VERY family orientated and love nothing more than a get together over a lengthy meal whilst the kids run around near them. People who have a sword also like to uncork the champagne by slicing the cork off.
There are many more simple customs and traditions , for instance you never go empty handed when you are invited for a meal and take flowers, a gift or chocolates for your hostess. You give small sums of money to children on New Year's day called "Etrennes". Some girls celebrate Saint Catherine's day at the end of November especially when they have reached the age of 25 without being married, St Catherine being the saint girls appealled to to find a husband.
The French also wish people a happy day when it happens to be someone's name day, and not just on their birthday. One always says "Bonjour" when entering a shop or starting a conversation with a shopkeeper and "Merci" "Au revoir" when leaving even if one does not buy anything, and when arriving at someone's home people always offer you a refreshment of some sort when they invite you in, as a matter of elementary courtesy.
You can take your pick from any of these. Good luck!