Ensure you have activated the side-quests listed previously before landing. As you land in Omega you will have to pick your squad. With still only two options, Jacob and Miranda, you must take them both with you. As you leave you may also have to level up both your Shepard character, and that of your allies. There are three main tasks in Omega:
Recruit the Veteran (DLC character)
Recruit The Professor (Dr. Martin Solus)
Upon arrival a Batarian named Mokkari will introduce himself, requesting that you head to the Afterlife nightclub (do they have nightclubs in space?) to meet Omega's main player, Aria. She will be willing to answer your questions. You will also be told that Dr. Martin Solus is currently involved in a quarantine operation in the city's slums. As Aria's case seems particularly urgent (and she's a powerful alien), you may as well head to Afterlife. Before this, however, if you purchased a new copy of the game and have downloaded the DLC (you should have got a code with the game to do this for free – you can activate it all via the game's main menu), there is a new character to recruit to your party.
A map of Omega.
The next chapters of this guide deal with recruiting the Veteran, Archangel and The Professor.