In the beginning take your time to set up the fingering of the chords and strum them smoothly. After a while the syncopation and speed comes naturally. There are some great exercises that you can do like this one:

|-----------------------|
|--4--7--5--8--6--9----|
|--5--6--6--7--7--8----|
|--6--5--7--6--8--7----|
|--7--4--8--5--9--6----|
|-----------------------|

If you keep going up the fretboard like that, and try it on different strings - it works very nicely.

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