We have a new Agent-centered guide up, covering such topics as your first agent in EVE, standing, important missions and many others. Excerpt:

Agent Levels in particular dictate the agent's overall quality, as well as the difficulty of the missions provided. A level 1 agent will give out missions suitable for new pilots in frigates, while level 4 missions are extremely difficult to do alone, with many requiring small groups of people to do. While it is possible to solo level 4 missions, it requires significant amounts of experience and expensive ships and modules.

You can find it along with all our other guides here.