What i have found works for me is:
-Deep conditioning overnight beforehand for moisture.
-Blowdrying gives a smoother flatiron.
-Using a really hot ceramic iron.
-An after DCing do not apply any product except for Chi Silk Infusion.
-Wrap at night and do a silk wrap the next day.
-Do Not under any circumstances use any products that have water or a humectant as an ingredient. Those products cause crazy frizz for me.
-Baggy ends at night with a little castor oil.
I have thick, fine 3c/4a ish hair.
I did 2 BKTs earlier this year and although my hair was
Glorious! I did experience sever breakage after the fact.
If you do a BKT dont overdo the heat and make sure you take extra, extra care of your hair after. I didnt really do much to mine and my ends were really brittle.
Looking back I probably shouldnt have done the BKT 2x and should have been more into taking care of my hair because now I am paying for it with uneven ends.
I did like the BKT though. It made my hair feel really nice and my flatiron lasted for 2 whole weeks with zero frizzing and zero reversion(which I have never been able to achieve before.) My curls are a little looser after as well and clump together better. Which I think is a plus... Minus the breakage...
All in all, be very careful if you decide to do a BKT, without I was usually able to keep my hair nice for a good 4 days with my other steps.