Sound Check
At first the right hand should pluck the strings one by one, from top to bottom, to verify that each string sounds right. You can do it four times on each chord, it is reasonable at first, but then should reduce if possible to only one strum by chord, which would force a very fast chord changes. If it costs too much, it is not necessary to do so, but must be changed with relative ease before moving on to practice of a strum, like the zamba.
Focus on the right hand
To practice the strum, at principle should forget about his left hand for a good execute. Then, while always maintaining the same position of your left hand (or the same chord), perform the necessary strums with his right hand, very slowly. Once you know how to do it, go speeding up its execute until you can do it swiftly and without thinking.
Piano, piano, you go lontano
A well-known expression, which it means advancing slowly for better results. As in songs usually are executed a few beats to each chord, you can practice strumming as if you accompanied a song that has two chords that change every two bars. Start with a tempo very, very slow to make the change without missing a beat. No matter if there are no zambas so slow, at this time you are not accompaning, you are practicing. This is much better than doing it in real time, and stopping to change the chord. However if it does well in a slow beat, all you have to do then is go accelerating slowly the velocity, without missing a beat, up to execute in real time.
Listening to those who know
The professional versions are very illustrative of how to run the accompaniment of a song. A good exercise is to play along with a recording to keep pace while making the chord changes.
Anyway, in the tutorial of this course there are some songs that are taken as a model of learning practical accompaniment, including a sound version in MIDI format to facilitate practice.
