How do you knit twice into yarn over?

Usually the pattern you are working will tell you the preferred method.

Typically it is done through knitting into the front and then into the back of a stitch.

A regular knit stitch is done like this:

Put right-hand needle through the right-most stitch on the left needle, wrap yarn over right-hand needle, pull stitch through, and pull loop off the left-hand needle

A knit stitch through the back is done like this:

Put right-hand needle through the right-most stitch on the left needle on the back side of the needle (that's from the right side, but catch the back side of the loop) , wrap yarn over right-hand needle, pull stitch through, and pull loop off the left-hand needle

To do them in the same stitch:

perform a regular knit stitch, but do not pull the loop off the left hand needle (if feels very awkward, but don't panic), then put the needle through the back of the loop and complete the knit.

The end result is one more stitch than you had before.

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