I just downloaded the sheet music to Gershwin's Prelude 1. Ohmygodwishmeluck.

But, seriously, the best way for me is to listen to the piece many times, and also to try to SING it. It doesn't matter if you sound like a hoarse crow, just hum and sing. I count the bars if I have to investigate the rythm from the beginning (and I count 1/16 if I have to, because I don't want to get the syncopes inbetween my counts ...)
If I don't get access to a recording, I can make one myself on my digital, in a very, very slow tempo and using the metronome as a counting tool (see above), and then I play it back in a faster tempo so that I can hear the rythm and "get it into my body" - I mean, at least I don't count when I have learned a piece half-way, then I just feel it inside.