To begin with, he should limit the initial setting . Most science fiction games are set against a broad canvas of many inhabited planets. A good way to think small is to keep the characters on a single planet for a while. That way they can become familiar with it and its inhabitants before moving on. Doing makes it easier for the GM, as well as they players.
Smaller settings are much more manageable.
Less preparation is required to create and detail a single world rather than dozens of them. Remember also that a single world can be huge. Look at the diversity and breadth of life on Earth. There s no reason Epsilon Eridani III need be any less interesting. Some SF games are entirely Earthbound.