What the funk?
Start with basic 16th up-down strums.
When you have it down, mute some of the strums to create "holes" and "spaces".
As you progress You may consider laying out the whole 16th up-down pattern and just hit the parts where you want it to 'funk'.
If your strumming makes your head bob and makes you want to dance, you've nailed it.
Remember, less is more. If you listen to seasoned players (Jimmy Nolen of James Brown, Steve Cropper, Ohio players, EWF guitar players, P-Funk, Sly and the Family Stone, etc.), they don't fill up the whole spectrum. Just a little bit here and there.
Try sliding 4ths (Hendrix style) or doubling the bassline. Diads and triads work better than full chords, just make sure the intervals ring (usually, Dominant 7th, Sus Chords, 6ths + 9ths). The Hendrix 7#9 chord (Purple Haze) is also a staple in the field of funk. Try different inversions. Though he is not funk, Scott Henderson plays with lots of it if you closely listen to his playing.
Though it is common to plug through your wah/ phaser to achieve the vintage funk, these are secondary - the rhythmic aspect and intervals always conjure the funk. A ringing clean tone works best for that.
