In English, preposition use is often about idiom not grammar. It's simply more natural to say "important for" or "important to" rather than "important of". Similarly, "It's kind of you," is generally more idiomatic than, "It's kind for you".
Once you get past the basic grammar, it's a good idea to memorize English phrasal verbs as well as common verb-preposition collocations. Simply memorizing the verb itself isn't enough. In the same way memorize common patterns with certain words, for example:
"happy" + infinitive: I was happy to hear that she got a promotion.
"happy" + for [someone/something]: I was happy for her that she got a promotion.
That being said, I think some of your examples are of different sentence structures. "For" can introduce a relative clause, as in your third example, which can be rephrased:
It is important that the meeting start tomorrow.
Be aware that words often pair with several different idioms, but with slightly different nuance.
It's silly of her not to accept his offer
implies that she is being silly, for the given reason. Meanwhile
It's silly for her not to accept his offer
implies that the given action or reason is silly. This may seem like a trivial difference, but in some circumstances it might be offensive to call someone silly, but less offensive to suggest that they are making silly choices.
You can apply this to other terms similar to "silly". Imagine (at some time in the past) a royal counselor speaking to the king or queen of England:
Your Majesty, I believe that it is unwise for you to provoke war with France at this time.