Bossa Nova is actually not the name of a particular style. It's a generic term used to refer to the "new beat" style that came to North America from Brazil in the late 50's. The "classic" bossa nova beat is actually a slow samba. The samba beat is characterised by a drum called the SURDO.

The surdo beat is very simple: in 4/4, a high-pitched, short beat is played on "1" and a big booming beat is played on "3". Actually, in the 2/2 time that bossa is felt in, it's on what is then called "2", but most North American charts (for example, the "Real Book") notate it as 4/4.

To simulate this on bass, we play the root as a short note on "1", and play the 5th with an accent on "3". It's preferable to drop DOWN to the 5th when practical