Watch the The Man In Black online guitar lesson by Angus Clark from Hard Rock Survival Guide: Rhythm
Blackmore had a writing/playing style that favored two distinct approaches: 1. Power chords (played as fourths) from within the minor pentatonic scale; and 2. Octaves outlining a more classical sounding progression that favored bVI - bVII - i, or bVII - IV - i, with some kind of turnaround on the V chord. So I've used this deconstruction of the style to help me create a rhythm part in the style of. It's a great exercise for your own songwriting. It's called an emulation exercise. From a rhythmic standpoint, there are some syncopations in the riff part that are specifically anticipations - you are playing on the off beat preceding a downbeat, and you hold through the downbeat. If this is tricky for you you should spend some more time with the metronome to get it tight. Remember to set your metronome at the quarter note or half note to the tempo you are playing. That way you are providing the time - not the metronome. On the technical side, watch my right hand and how my second and third fingers are glued together when I am executing the fourths during the riff section. During the root-fifth-octave section, note the way I release each string when I move to the next string. This will keep the part really clean.