Paying close attention to fabrics and textures helps as well. A textured wool pant with navy silk shirt and black cashmere cardigan- perfect. Vary your fabrics and textures and it will be a bit easier to work with! Additionally- I think it is a good rule of thumb to make sure you have at least two items in each color- again so it looks purposeful. There are exceptions to this rule- but you have to know what you are doing.
Also- if you are beginner stick to lighter navys as opposed to very dark "off black" navy items. Finding key items that have navy and black in them- is helpful also. I have an adorable pair of navy flats with a black patent leather toe and black bow. Additionally, I just "treated" myself to this adorable coat from forever 21 that is the perfect combo of navy and black- for a mere $35. How could I not?
Courtesy of Polyvore, I put together some suggested navy and black combos for weekend, work and party situations.