If you're a loose knitter, it's easier for DPNs to slip out. I'm a loose knitter.
Wood needles usually have more grip than metal needles. You can also try not to swing the work around as much and keep it more stable. Resting it on a table top or desk that you sit at, on top of a pillow in your lap or on top of a pillow on a table top can help. Those all help me.
My favorite thing to do is use circulars whenever possible and only use the DPNs when I absolutely have to. There's even a technique for knitting socks with a pair of circular needles. You could also check that out.
Wood needles usually have more grip than metal needles. You can also try not to swing the work around as much and keep it more stable. Resting it on a table top or desk that you sit at, on top of a pillow in your lap or on top of a pillow on a table top can help. Those all help me.
My favorite thing to do is use circulars whenever possible and only use the DPNs when I absolutely have to. There's even a technique for knitting socks with a pair of circular needles. You could also check that out.