Common vocabulary: how to handle

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This is a problem you will find in any language, but I will only focus here on the language I know to talk about the problems of common vocabulary you may see.
The most common vocabulary is the one used in conversations. Meanwhile it varies greatly depending to who you talks, basically, they will use mainly "passé composé", "présent" and "futur". The conditionals are also common, but outside of that, you don't have to spend too much time on other times in the grammar, they will be used less.

As well, the set of words will be kept simple in conversations, meaning that even if there's expressions and the like, you wouldn't see much words from the old French, or from the manuals you will read. Rather, read some French conversations and notice the word you will hear often. People learning tend to speak too much in "Louis XVI" language.