The Elder Scrolls V: Skyrim Tips

Thieves Guild - Faster Additional Jobs
This will help you get through Delvin's and Vex's additional jobs faster, and make it easier to boost towards the City Influence quests to restore the Thieves Guild back to it's former glory. First off, always take a Bedlam job from Delvin and a Heist job from Vex. Make sure they're both in the same City hold that you haven't done a City Influence quest. This is either Whiterun, Solitude, Markarth or Windhelm. Riften will not count towards the City Influence quests.

When you ask for the job, wait for the Objective to pop on-screen after confirming your job choice. If it's not in the City Hold you prefer, simply talk to the respective employer and quit the quest. Repeat as necessary until you get the right city. Don't worry; there's no ill-effects from constant declining.

Now, with the two jobs in that area, simply go and complete the Heist job. For a majority of the time, you should collect the required sum of the Bedlam just from completing the Heist. Rinse and repeat.