What are the most common symptoms of astrocytoma?

That depends. Astrocytomas come in many flavors. They produce symptoms by local brain invasion and compression of adjacent structures as well as increased intracranial pressure. The clinical symptoms depend on the involved areas of the brain. Headache is the most common symptom. This does not mean that every headache is a brain tumor. Suggestive signs are nausea and vomiting or a change in headache pattern.
Several. Unexplained seizure. Personality change first noticed by the person's partner. Both are likely to precede headache.