Just because you have six strings, doesn't mean that you need to play them all every time you strum. Help yourself to a great habit early on by learning how to zero in on specific strings that you want to play. 

On chords like E and G, as well as most barre chords, you can freely strum across all six strings, but when playing 5-string chords like A and C, it isolates the chords root better if you start your down-stroke on the fifth string.

For the D and F chords, try to start from the fourth string to help better isolate the chords root. Targeting your strumming like this helps you develop picking-hand discipline that will stay with you forever.



ISOLATED STRUM HAND TECHNIQUE:
- Open Chords -

Our first exercise will look at isolating 6th-string open chord roots, with our goal being that of targeting the root note of the 6th-string (since it relates to the naming note of the chord).

In exercise one, the goal is to hit all chord tones on the down-strum, and clip the upper three strings with the up-strum.

Exercise #1). 6th String Strum Isolating (G Major to E Minor)



NOTE: You don’t have to hit all the strings on your upstroke. When you hit the bass strings on your down-stroke, they’re going to ring out for a long, long time. Then, when you make your upstroke, just hit two or three of the high strings. That will be all you will need to execute the tone of the chord on the up-strum. Also, striking only a few strings will allow you to get your hand in position for the next down-stroke strum.




In exercise two, we'll switch to the chords that are rooted off of the 5th string. These chords are to be approached in much the same way as the 6th string root chords. Make sure that the down-strum attack includes the chords root off of the 5th string and catches as many of the other strings in the bass as possible to project the dynamic of the chord on the down strum.

On the up-strum, be sure to include two or three of the upper strings. These strings are the lighter follow up strum to the down-stroke strum. The idea is to once again, "clip" the upper chord tones and apply a lighter dynamic across the up-strum.

Exercise #2). 5th String Strum Isolating (C Major to A Minor)



In the third example, we'll isolate even fewer string sets with our strumming attack targeting the 4-string chords of, "F Major," and, "D Minor."

The down strum needs to dig into the root and grab at the low tones of the chord. This presents the chords color on the down stroke and builds the initial dynamic and punch into the chord. The up-strum is once again much lighter, and only catches the upper few strings.




Exercise #3). 4th String Strum Isolating (F Major to D Minor)



The isolation of so few strings in the 4th-string chord category means that your strum movement must be extremely tight and extremely accurate. The movements need to be as precise as possible to avoid clipping any of the lower (5th or 6th) strings.

To develop this, watch each hand (left and right), as you practice the strum attacks.

Be sure that your strum movement occurs from your wrist and keep a relaxed grip of the guitar pick between your fingers so as to control the pick "attack" into the strings.


CONCLUSION:
Over a period of time, (and practice), this type of isolated strumming will become much easier to perform. The long term result will be far more control over the strumming movements and a much better sound. The by-product will also be greater ease for playing many different styles of rhythm guitar.