What is a smile? It's bearing the teeth. If you think about it, it can be a hostile action. A smile is a bit like a dog growling and baring its fangs to threaten (without the growling and drool). Ah, but the eyes tell the story. As well as the rest of the face. Is the face scrunched up? Are the eyes glaring? The nostrils flaring? But there are cold smiles as well - that sickly sweet insincere smile, or, worst, the calm, eerie smile that can send shivers down your spine. Humans of all cultures can identify, on average, what is a happy face, a disgusted face, a mad face, and so on. Our ability to read faces crosses cultural and racial boundaries. But we are talking humans. What about non-humans?
Will aliens have the same range of emotions, or with the same intensity? Will they communicate emotion more with voice tonal differences, or with light, rather than by physical appearance? What if their faces have fewer muscles than ours, limiting their ability to communicate via facial changes? For them, a happy face could be one that is frowning. And a smile can be threatening.
Even simple gestures can be misread. Even here on Earth: the Japanese hand gesture for "come here" looks too much like a "scat, go away" gesture for Americans. How much more can gestures be misread by aliens (and vice versa)?
Those involved in first contact will need to pay attention to details, and think fast on their feet yet also be patient, and not easily insulted. But that is asking a lot of such a person. I think first contact is best done by learning all you can before hand - eavesdrop on their broadcasts, learn their language, their culture as much as possible via probes and listening devices. Even then, there will be pitfalls.
But if we travel out into space, we may meet new races of sentient beings without the benefit of learning some basics about their language and culture - we may be meeting them for the first time. First contact is probably dangerous, difficult business. It would be great if we had mentors, other alien race(s) who would help us as we spread our wings further and further away from our home nest, the Earth. Otherwise, I hope the aliens we meet for the very first time are also cautious, and willing to not take offense to mistakes, and to especially resist taking personal any offense. If first contact can be difficult on Earth between sentient beings of the same species, just how much more difficult will it be with another race of sentient beings?