Tips for newbie to Washington (Washington, D.C.)

Hi,
I'm moving to Washington d.c. in the next few weeks and am currently hunting for an apartment to rent. Was wondering if anyone could please help with advice on what areas are good to live in/close to work (I will be working downtown) as well as tips on available flats. Have never been to d.c. before and appreciate any advice you may have.

Many thanks!