There are a few users giving general tips in discussions. I figured to help one finding its way around them, I'd reference them here. I'll add more as I find them, or if someone stumble upon one, please tell me in my stream or in this discussion and I'll add it here.

• <h1>Nouns :</h1>

  • Garçon;

  • Fille;

  • Gender of nouns, and a few good guesses for the gender according to their ending;

• <h1>Verbs :</h1>

  • Tips for conjugations in the present tense, including the difference between sont and sommes;

  • How to conjugate all the French verbs;

  • Step by step learning of French verbs;

  • C'est, ce sont vs il/elle est, ils/elles sont;

• <h1>Articles :</h1>

  • Possessives articles;

  • Partitive articles (Des vs De);

  • Partitive articles (De vs Des /Un /Du /De la);

  • Definite vs Partitive articles (Les vs Des);

• <h1>Pronouns :</h1>

  • List of many personal pronouns;

  • Direct and indirect object pronouns;

  • Reflexive verbs and the pronouns used with them;

  • Ce, ces;

• <h1>Adverbs :</h1>

  • Ici, là and là-bas

• <h1>Prepositions :</h1>

  • Different uses of en, preposition and pronoun;

• <h1>Conjunctions :</h1>

  • Depuis que, how does Duolingo handle these sentences and expects you to translate them;

• <h1>Pronunciation :</h1>

  • General pronunciation of French letters and group of letters;

  • Tips for the pronunciation (or not) of the final letters in French words;

  • Pronunciation of the letter y;

• <h1>Other, general help :</h1>

  • Words you already know in French if you speak English, or true friends or cognates;

  • A (wannabe) compendium of simple tips for complex grammar rules, including a tip for verbs endings in all tenses;

  • Charts, for those who like the visual way of learning.

  • Another French grammar reference, very complete with sound files to help grasp pronunciation as well.