Here's a little thing I put together to develop the 4:3 cross rhythm/metric modulation in jazz. Normally you actually want to explain an advanced concept like this, but really, if you don't recognize it right away, you're not at a stage where you should be working on it. Improperly applied, it's a recipe for all kinds of bad playing. Plus I screwed up my back a little bit today, and oddly enough explaining things makes it worse.
So here we are- basically I've translated the first batch of exercises in Jim Chapin's Advanced Techniques into dotted-8th pulse:
I recommend running each line very slowly, counting out loud in 3/4- the hardest thing about this modulation is remembering the original pulse. You could also do a few measures of jazz waltz time in between exercises.
As it gets more comfortable, put it into 4/4: count two lines of exercise as three measures of 4/4 (still counting quarter notes- at no point do you count in the "implied" meter). Then play one (or three, or five) measures of jazz time in 4/4 and then two or four repetitions of each exercise.
Download the pdf.