Graham,
I'm with you, having difficulty. I'm trying to play "Take Five" (and probably obviously as it's the only 5/4 tune I know of).
Quick answer is practice, practice etc, but in my mind I'm trying to group the last beat in the 5 with the first beat in the next bar to make a 2/4 phrase (each note has a different chord) and then group the next three, which have the same chord as the last of the previous 2/4. That seems to match the rhythm of the piece. Then back to practice, practice.
Good Luck
Keith