When the French write in their own language, they unconsciously respect a large number of grammar and spelling rules (well except for some people who make a stunning number of mistakes, but let’s concentrate on those who can write correctly). Most of the time, they do not need to think about it; but still, sometimes we have to remember the lists and techniques learnt in our childhood. Here is an overview that will give you an idea of what is learnt in a French primary school.
Feminine words in té and tié
They do not end with an e (l’amitié, la bonté, la beauté, la saleté). There are some exceptions however: capacity nouns and five everyday nouns: dictée, jetée, montée, pâtée, portée.
The m, b, p rule
In front of the letters m, b and p, the letter m replaces the letter n (exemple, emmener, jambe). Some exceptions: bonbon (et bonbonne, bonbonnière…), néanmoins, embonpoint, mainmise.
Er or é? Try with a third-group verb instead!
Is it « je dois parler » or « je dois parlé », « il est tombé » or « il est tomber »? If you don’t know the answer naturally, you can do like many French people who use what they have learnt in primary school: replace the verb by a third-group verb (mordre is the most frequent). You will then see that it is « je dois mordre » and that you need the infinitive and « il est mordu » with the past participle.
Mais où est donc Ornicar?
This sentence is a trick to remember coordination conjunctions: mais, ou, et, donc, or, ni, car. A lot of French people remember it, and it was even a Facebook page and is the subject of very strange videos on youtube!
I believe these rules and tricks to be the most famous for French people. I have probably forgotten several, and would enjoy reading your primary school memories!