This is not so much a tip as it is a suggestion. PATIENCE...I think patience is the key when using feathers. Don't just give up after the first few strokes with no reaction. I would give it a good minute, at least, of stroking, flitting, and dancing the feather all over the sole of the foot. Try to keep the movement pretty vigorous and random, and make sure you don't forget about the toes. The tops of the feet, and around the ankles, can be very ticklish too, and they can get the ball rolling for the sole...if you get my drift.
My wife has gorgeous feet and I love to tickle them, but she isn't the most ticklish person in the world. Ironically, it is very difficult to get a rise out of her using my fingernails. Feathers though, usually do the trick. I first discovered this by accident. We were fooling aroung wrestling one day and I got her pinned on her stomach. There was one of those cheap $1.50 green feather dusters nearby so I grabbed it, locked her feet under my arm and started tickling her with it. I truly didn't think it would cause a reaction at all. She goes barefoot alot, and as I mentioned before was becoming pretty resistant to my tickling her with my fingers, and the feather duster just seemed too soft. She wasn't fighting me too much to start with, so I kept using the feather duster. After about thirty seconds, she started to squirm, then she started to giggle, then came the laughter and kicking. I couldn't believe it. It was actually tickling her. I have since found feathers, here and there, of all types to add to my small collection. She allows me to put her in light bondage. Which frees up both of my hands. I usually start with softer feathers, not the super soft ones, but feathers like the ones that come off a cheap feather duster. If I can get her going with those, she is in trouble. If not, I will graduate up to stiffer and stiffer feathers. I have a very pointy wing feather, off of a turkey vulture, that is deadly. I always use it, but I usually bring it out as the finale. When I get that baby moving up and down, under and between her toes, she always responds quite favorably.
Feathers have now become my favorite tickling tool. In fact, when I am trying to coax my wife into the bedroom, I will playfully ask her if we can use "tools". She knows that means I want to tickle her feet with feathers. She doesn't share a love for tickling, but she will allow me to tickle her periodically, and I do think I have imprinted a mild Pavlovian response to it in her. But don't forget, you have to be patient. If you are pressed for time and not sure how your ticklee will react, you might start with a stiffer feather. Keep it moving and don't give up too soon. Good luck.
Gallodiablo