Straps should be across the hand rather than over the wrist (they will come up into the crease of the wrist a bit - they just can't be so high that they prevent the wrist from extending when overhead in a snatch, for example). Other than that, you can pretty much do what works. Typically the strap is wrapped from outside toward inside (i.e. comes off the hand under the bar and goes around the bar in the direction of the thumb), but sometimes I will thread the end through the loop when snatching because it gives me a better hand/wrist position overhead. For pulls and DLs it doesn't matter much how it's wrapped as long as your hand isn't smashed down against the bar so much that your wrist can't remain about neutral.