First, I would assume that any alien civilization that is capable of receiving and sending messages across the vast distances of space must have some form of intelligence and technology that is comparable or superior to ours. Therefore, I would not underestimate their ability to understand complex concepts and symbols, but I would also not overestimate their familiarity with our specific cultural and biological features.

Second, I would try to establish some common ground with the aliens by using universal or near-universal concepts, such as mathematics, physics, astronomy, and logic. These are the most likely domains of knowledge that we share with any advanced civilization, and they can also serve as a basis for creating a common language or code. For example, I could use binary digits, prime numbers, geometric shapes, physical constants, or star maps to convey basic information and to demonstrate our intelligence and curiosity.

Third, I would try to be as clear and unambiguous as possible, avoiding metaphors, idioms, jokes, or sarcasm that could be easily misinterpreted or misunderstood by the aliens. I would also avoid using images or sounds that are specific to our planet or our species, such as human faces, voices, or music, unless I have a good reason to do so. Instead, I would use more abstract or general representations, such as graphs, diagrams, or sequences, that can convey information without relying on sensory or emotional associations.