Mercury in the 1st house shows a very lively, active, and of course, communicative person. Such a person is very restless and actively responds to any contacts, to everything new. It is difficult for him to sit still, he is very mobile. Curious.
Contacts are very important for such a person, but of course, we also look at the 3rd house - if it is tense, then it is more difficult for him to maintain constant connections with friends. He either constantly communicates, or is looking for some information, or reads, or travels somewhere. He needs food for the mind, new impressions, new information. And this information is either external, that is, through speech, through contacts, or it is the topic of learning, immersion in new knowledge or new research. Of course, we look not only at the planet, but also in what sign it is. For example, a watery Mercury will react to emotional topics, while feeling the interlocutor well, contacts will be more heart-to-heart, with a rich imagination. An earthly Mercury will be distinguished by business contacts, communication on the merits. But in whatever sign it is, such a position of Mercury will give a person a huge liveliness of mind, mobility, sociability.
With Mercury in the 1st house, a person often looks younger than his years. And even with age, this youthfulness is preserved.
With such a position, a person may manifest Mercurial professions, where a lot of communication is needed, something needs to be connected, someone to be introduced, somewhere to go - consultants, journalists, secretaries, salespeople, writers. But we always take into account the houses of professions, how Mercury is connected with them in the chart, aspects, which houses it rules