I vote just getting some pretty [multicoloured] yarn, and knit a tube! You'll get the hang of DNPs without having to worry about aaaaaaanything else like a pattern, or gauge. Then once you get the hang of working with four or five needles (try having your work on three needles for a bit, as well as four needles. I found someones using the extra needle just gets in the way and makes me angry, while other times, it's too hard to manage the stitches without the fourth needle. If you keep knocking into the other, flopping needles, switch to three, for example)
The reason I love this way so much, is because you can do whatever you'd like with it! Want to knit four inches of straight knitting, and then give ribbing a try? Why not! Feel like throwing in a heel just to get the mechanics of it, what's to stop you? Knit a bit in the actual leg pattern of your sock, and then think 'what the hell, I'll finish with a toe'? Even better! You just made yourself the weirdest shaped sock of all time, congratulations!
And once you're done, you can rip it all out and reuse the yarn for something else. Or keep it for a laugh, doesn't matter either way!