I do a lot of grafting - top to top, top to bottom, stockinette to stockinette, reverse stockinette to reverse stockinette, and even rib to rib. There's one rule of thumb that holds true in every one of these situations. It doesn't matter if you knit continental or combination, and it doesn't matter which way the stitches are twisted on the needle. ALWAYS:
enter into the knit side of the stitch when crossing from row to row,
enter into the purl side of the stitch when crossing from stitch to stitch in the same row.
Or think of it this way:
Use the front door (the knit side) when going across the street (to the next row).
Use the back door (the purl side) when going next door (to the next stitch).
For instance, if grafting a 1 x 1 rib, when working from stitch to stitch in the same row, you've entered the first stitch through its knit side and thus exited through its purl side. If that purl side is on the bottom of the fabric, then bring the tapestry needle to the front of the fabric to enter the second stitch through its purl side, exiting on the bottom of the fabric through its knit side. Then across to the other row to enter the stitch there through its knit side.
That's really all you need to know. It works in every situation where a knitwise graft is called for.
For a purlwise graft, as for garter or seed stitch grafting, do just the opposite - enter the purl side and exit the knit side.
So simple, you may actually start to enjoy grafting!