Play eighth notes on the snare drum using both single and double strokes
1 + 2 + 3 + 4 + r l r l r l r l r r l l r r l l
Now play the same pattern around the kit as follows
1 & the + of 1 on the snare drum 2 2 small tom tom 3 3 medium tom tom 4 4 floor tom tom
Your bass drum is keeping time with the quarter note pulse throughout the fill.
Now put the fill into a musical context by playing three bars of an eighth note rock groove followed by one bar of the above fill and then back into the groove etc etc. The timing of your right handed eighth notes on the hi-hats and those around the kit should be identical.