How to: Freelancer Career Cheats
Press Control + Shift + C then type testingcheats on and press enter. You can now get promotions with careers.promote adult_freelancer_artist, adult_freelancer_agency_writer, or adult_freelancer_agency_programmer - you can also see all our Cheats. If these do not work for you try careers.promote artist for example

Become a Freelancer by using your phone. You can be a Freelance Writer, Artist (Painting), or Programmer. You'll take on an agency tailored to each type of job. All three will need the computer to work, though the artist will do the big stuff on the digital sketchpad (find it in misc electronics).

Rank Up As a Freelancer

Despite the differences between Freelancer and a normal Career and the freedom it brings, you still have a performance meter. You start at level 0 and with each rank, you'll get an additional 10% pay on top of what you would normally get for a gig. In addition, the client may toss an extra 10 or 20% on top of what you're getting if they really like the work. When you rank up for the first time, you get a small reward in the form of a freelancer plaque to hang on the wall as well as an object or two that you'll find in the family inventory of buy mode.

Ambitious Sims get a boost, a big one, toward performance. Lazy Sims actually take longer to rank up. These are the only two traits I saw impacting the career. Emotion still matters and will boost the amount of performance you gain when you finish a gig, though I cannot tell exactly at what stage it's important to be in the right mood. Regardless, you should have little trouble becoming a master at your chosen field.