I think that "Do not act like a clown" is better than the second one. "Don't clown around" also works. However, the idea of "Do not make a clown of yourself" is used commonly in English, but is more often expressed "Do not make a fool (out) of yourself." I hope that made sense.
Italian pronunciation is usually pretty straightforward: it's something like pah-LLIAH-cchoh, with the second syllable being stressed (not so evident in the duolingo sound). The Italian "gli" sound isn't common in English though, and isn't pronounced exactly like a double L; this link has a few examples of pronunciations, but only as sounds: http://languagespeedway.com/page/official/italian/pronunciation6gnandgli
As I see it, in affirmative sentences like this one, the verb comes second (tu sei..., tu fai... etc.). In questions, depending on emphasis or meaning, it can be in both orders, like in the conduttore phrase: "Sei tu il conduttore?" vs "Tu sei il conduttore?". Boh are correct, but have a slightly different meaning.
As a native English speaker, I would hear and use 'clown' much more often as an insult.....somewhat equivalent (though maybe less harsh) to idiot. To a child being silly I would more likely say something like 'acting like a goof' or maybe 'being a monkey'. Am I understanding correctly that in Italy, this would not be used as an insult?
yes.for example,there are many clowns in the italian parliament!!but you can find them around for the streets too!