Here is a worksheet you can use to develop steady 8th and 16th notes around the drums. I've structured the page so that you begin by warming each hand individually playing 8th notes (aka "8 on a Hand") and then you add your opposite hand for single stroke 16ths (ala "Chicken and a Roll").
Once you are able to play this rhythm with a steady beat on the snare drum, it's time to move the pattern around the set. First we do this with our "skeleton" 8th note rhythm, and then later add the 16ths like we did before on the snare.
Finally we put the exercises in the context of a drum beat that we play for 3 measures and on the 4th measure we play our "fill" - either the 8th note skeleton or the 16th note pattern. For your main drum beat, I suggest using drum beats from a book like Rod Morganstein's The Drumset Musician or Joel Rothman's Basic Rock Beats.
Suggested tempo is 60 - 80 bpm and focus on getting a nice and relaxed rebound stroke as you play these exercises.