I found that breath attacks, followed by barely tonguing progressively evolving to more aggressive tonguing helps me on that. The tongue should be as light as possible. Whenever I work on difficult (for me!) articulations, I try to cover all the spectrum between sharp attacks and totally slurred, then try to gravitate where the piece should be. Overall, I must say I find it easier to tongue lightly with multiple tonguing than single, although everything gets more difficult around Bb above the staff. I sincerely think that this is one of these things that holds many yet-to-discover dimensions one can only uncover with lots of practice.