I know exactly what you're talking about--the tray isn't high enough above the seat for me, so my legs push it up, resulting in a sliding effect. I don't have any great advice, but what I do is first, make sure everything in my pockets (especially my wallet) is out of the way of the tray. Second, I'll make sure I'm sitting as straight as possible (in other words, not reclined.) If all else fails, I'll hold on to everything with one hand while eating with the other--a bit uncomfortable, but hey, it's not like I'm not exactly eating a gourmet meal anyway! Hope this helps a little.