The Yin and Yang of practice for me are:
1. make it FUN! That's the whole point.
2. have some sort of FOCUS, that makes sure you develop/improve over time. This could be timing, single strokes, double strokes, kick, double kick, new styles, a cool phrase you heard and want to learn, stick control, whatever. More abstract, but this is how you get better.
Depending on how much practice time I can carve out, sometimes I do both, sometimes I do the other. My favourite practice sessions go like this:
1. Sit down and just play for a while, whatever you feel, get warmed up
2. Work on a chosen 'development'/focus item, with discipline. Keep at it.
3. After a while, develop your 'focus' idea further, for example: If your focus is hands, keep going but begin adding feet after a while. If your focus is feet, begin adding hands too after a while - develop the idea, looking for a way to fit it into your normal playing. Keep going back and forth gradually between 'more focus area' and 'more real playing'.
4. Now just play some more!
5. Depending on how much time/energy you have, repeat from 2 with another focus area.
This can last anything from 30 mins to hours...