Here's a five against three polyrhythm as I explained it to Andy. To get the hang of this, you're going to tap quarter notes with your left foot in 3/4 time (the red squares). Then you're going to tap quintuplets with your left hand (the black circles). Then you're going to tap every third beat of the quintuplet with your right hand (the blue squares). As you do this, count the quintuplets out loud, "one, two, three, four, five - one, two, three four, five", until you're very comforatable with it. Then you're going to stop playing the quintuplet with your left hand, but keep counting out loud. Go back and forth for a while between playing the quintuplets and not playing them. Eventually, you won't need them.
This technique works with everything. If you want to play 7:2 for instance, tap quarters with you're left foot. Then tap septuplets with your left hand. Then tap every other note of the septuplet with your right hand. Then stop tapping with your left hand. You'll be left tapping seven evenly spaced notes with your right hand, against two evenly spaced notes with your left foot.
If you want to play 5:2, tap quarters with your left foot. Then tap quintuplets with your left hand. Then tap every other note with your right hand. Then stop playing the quintuplet.
This will work with any tuplet. By playing the tuplet against the quarter note, then playing either every other note or every third note of the tuplet, you'll be able to figure out some pretty interesting stuff.