I use cuttings between 8 and 12 inches long. What you want is to have at least a couple of bud nodes below the soil and at least one above the soil. Make sure you scrape some bark off the bottom part and use a rooting hormone. Then the hardest part is keeping them evenly moist without drowning them or letting them dry out too much. And of course the waiting, lol!

I'm finally (I think) having some success with potting them into clear plastic cups and placing 2litre bottles over them (bottoms cut off) and misting every day. I also have them inside a chamber I made with pvc pipe frame and clear plastic over it, with clay hydroponic pebbles under them, kept moist and greenhouse heating pads underneath. I just checked the last batches and so far they look good after a few weeks. I cut the stems into 2 pieces when I pot them up. Usually, the bottom half of the stem won't have any leaves, or maybe just one. I still pot those up anyway. Even those are looking ok at this point. I put 2-4 stems in each cup. Depends on how many I end up with. Sometimes some of the bottoms of the stems are kinda weird looking and I'll cut them off. Also depends how many budeyes each stem has. A couple of the roses I tried had large spaces between budeyes, so I only got 12 cuttings instead of 18-24 (per dozen stems).

I just today potted up cuttings of a florist rose I've been trying to find for awhile. SWEET BERRY. I'm really excited about it and hope these cuttings work.

I sure wasted a lot of time, money and cuttings the last couple months trying the burrito method. Wish I would've just gone ahead and done what I'm doing now. As long as you keep them moist they should eventually take. I found that many of mine that didn't make it had gotten too dried out. So make sure you keep them moist!

Take a look at the link below and you can see how Dan roots his cuttings. He has a pretty high success rate.