Double sided knitting

I’m having trouble with the double-sided knitting (there’s a video of it in the ‘advanced’ section of this site using a white and red heart pattern). I’m using my own pattern, but i can’t figure out how to get it started. I might be casting-on wrong: I’m using the regular cast-on method. I guess I’m not really sure what I’m doing wrong, but every time I get going, both sides of my project feature purl stitches rather than knit stitches. Any suggestions??

Thank you,
Lindsay
(P.S. using straight needles, FYI)

Are you using two colors to cast on? This or this might help.