This is the pattern I've made up for my fake cabled arm warmers. Just a note, though: whenever I crochet in the round, my seams spiral a bit. This means that the FPDC's I did in this pattern spiraled, too. Yours may form straight lines down the arm warmer, which is what I intended in the first place

*These could be adjusted by chaining more to fit the width of your arms at the widest point the warmer will cover. If you do this, you'll end up working more or less than 9 DC around the FPDC/DC middle. They can also be as long or short as you want.
*Work only in one direction (no turning at the end of rows) until the pattern states otherwise.
*The pattern *should* start with the "wrong side" out. The wrong side here is the bumpy side of your DC (working in the round - you get one bumpy side and one flat side). If that's not on the outside as you start, just turn the warmer inside out and continue working in the pattern
Pattern (working from the arm end to the wrist end)
Ch 29 (includes one turning chain); join first and last chain to form a ring.
Row 1 - 3: SC around (28 SC), join, ch 1
Row 4: DC around, join, ch 2
Row 5: DC 9, FPDC 1, DC 8, FPDC 1, DC 9, join, ch 2
Repeat Row 5 until the arm warmer is as long as you'd like it to be, ending at the wrist. Then proceed as follows for the wrist/hand part:
Turn warmers right side out.
Row 1: SC around, back loops only; join, ch 1
Row 2: This part is tricky to explain. Now, you need to take your warmer and decide where the thumb hole will be. It'll be about 3 - 4 stitches wide. Slip stitch around to one end of the thumb hole. Ch 1, turn and SC around to the other end of the thumb hole.
Rows 3 - 5: SC across, ch 1, turn.
Row 6: SC across, join first SC of row to last SC of row (thumb hole is now made)
Now you can continue to SC around, turning at the end of each row, until the arm warmers cover as much of your fingers as you'd like them to.
Embellishment:
Decide what you'd like your "fake cables" to look like. You might want to draw them out, or use stitch markers to tell you where to place them. Whatever's easiest for you. Attach a new strand of yarn to the bottom of your work where the FPDC ridges start. Slip stitch through the top of the work in whatever pattern you've decided on.
FO, weave in ends, etc. And you're done!
I hope these directions are pretty clear. If you need help, just comment or PM me! And if you see any problems in the pattern, be sure to let me know.