The "bossa nova" right hand patterns are based on 
the "clave" figure. The example below is the first 
measure of the inverted clave.

Notice that on the guitar, the syncopation is played on 
the top voicew of the chord (using the right hand 
fingers 1, 2, and 3), while the bass note (played with 
the right hand thumb), comes on the beat.

Like samba patterns, the bass line usually keeps 
switching between the root and fifth of the chord, and 
it's a better choice to play the fifth below the root. If the 
bass note is already placed on the 6th string, you may 
keep the same note for the whole measure.

You can practice these patterns and variations muting 
the strings with your left hand. Try using "6/9" and 
"m9" chprds, II -- V progressions and their 
substitutions.

It's also a good idea to practice away from the guitar, 
clapping hands on the high voices and tapping the low 
voices with your foot.

Musical example is a transcription of the rhythm guitar 
part played by Joao Gilberto as the introduction for the 
song "Insensatez" (Tom Jobim), as recorded on the 
album "Joao Gilberto" EMI-ODEON, 1961