Clean both surfaces, I usually wash the area and then wipe it with some alcohol. Let it dry. Then apply the tape (probably to the ducts) and then place and hold some good pressure to be sure it sticks down. My preference is to then let it sit for a while before taking off down the freeway. It should stick just fine until you're ready to take them off.

I also use more tape than I should... I put as much as I can. I have had crap fly off in the past :/ but it's been a few years now and my eye lids are still OK!