Citadel: False Positives
This mission can be initiated by picking up a datapad in Garrus’s loyalty mission - Eye for an Eye (see the walkthrough page for the exact location).
To complete the mission, you will need to find someone who needs a false ID. Later in the game, after visiting the Collector ship, you can find a pair of Asari complaining quite loudly on a couch between the C-Sec offices and the western portion of the Citadel about travel restrictions. Speak to them.
If you feel like pushing up your Renegade points, you can give them the forged IDs straight away. However, if you want to improve your Paragon, you’ll need to head back to the transport offices right next to where the Normandy docks and speak with the woman behind the counter here. Tell her to ease the restrictions on the Asari.
Now, you just need to return to the Asari and give them the good news.
Citadel: Krogan Sushi
This mission can be obtained by overhearing a conversation between a pair of Krogans located near the Citadel Souvenirs shop on the Citadel. Once you hear the conversation, the side-task will be automatically added to your mission log.
To continue, you’ll want to travel to the Presidium and speak with the groundskeeper here. During the conversation, you’ll want to ask about fish in the Presidium ponds.
After getting the information, return to the Krogans whom you overheard previously and start up a conversation. Let them know what the gardener told you to complete the side-mission.
Citadel: Crime in Progress
This side-mission can be located on the western side of the Citadel, near the entrance to the Warehouse area you visited during Garrus’s loyalty mission. A C-Sec officer and a Volus are accusing a Quarian of stealing.
To begin the side-mission, get involved in the conversation to discover what is going on. Offer to help. After leaving the conversation, head over to the nearby store Saronis Applications and speak with the man behind the counter. Ask about the Volus’s credit chit to learn that it is in the store.
Return to the conversation and let them know where the chit can be found. This will end the side-quest and during the ensuing conversation, you can choose some dialogue options to increase Paragon/Renegade.