The rhythmic part of the Bossa Nova style is a mixture of Levels I, II and IIR of the Modular Phonetic Rhythm System by Chuck Anderson. This is the system I use with GREAT results.

Pattern One

Two quarter notes followed an eighth, dotted quarter note.

As Bossa Nova draws from a fusion of samba and jazz. With a rich harmonic structure of 4-part chords with upper partials, extensions and altered chords. I used a C6/9 chord for the example.

The hear the difference try it with an open position C chord, the first chord most ukulele player learn.

1-1 2-2
1 2 3 4

Pattern Two

1-1 2-2
1 2 3 4

Patterns One and Two

A the clave for a Bossa Nova is a two bar patter it is good to have two bar pattern.

First Eight Bars of The Girl From Ipanema - C

First Eight Bars of The Girl From Ipanema - Db

Db is lays pretty nice on the ukulele, especially with a low G, C tuning. It's a nice mysterious and dark key. Close to the feeling to the original vocal key in Ab of the original of 1964 Grammy Award for Record of the Year that started Astrud Gilberto's career.