One thing that is important when learning kips in a row is to make sure that the single kip is strong before connecting - straight arms, can make easily, can cast out of it (doesn't have to be high). Strong abdominal muscles and shoulder/arm muscles, like those trained for the kip, are good, though once they learn to do several kips they will quickly build up endurance in these muscles.
One thing our coaches did with us was they trained LOTS of straddle leg lifts, and straddle leg lifts from horizontal to make sure we would be able to keep our feet up on the kip, since lots of girls had trouble with this. We also did straddle holds, hanging from a bar, lifing our legs as high as we could.
I learned my kips in a row without drills. I merely wanted to be able to do them, since I already had all my level 5 skills and wanted to uptrain. It took me a little bit to figure out the correct swing that would give me momentum and put me in the right place to kip and keep my legs up. This was trial and error. When I watched the optionals to clear hip-HS-kip, I noticed that they lifted their legs really high in a straddle when they went under the bar, so I tried that too. I tried to just drop beneath the bar, not push far away from it, and to lift my legs so they were in a really high straddle.