First up is just letting her 'explore' this new thing - which means biting it and seeing if it is a plaything. It is afterall, a bit like slithery thing to catch, with some nice hard plastic bits to chomp on (she's teething). And once the thing has been well explored, and left out as part of her toys, I put it on her. I play it by ear as to how much is enough - it can be enough just to lay the harness over the neck and back, and maybe do up one clip. With both Ava and Kato, they didn't mind moving quite quickly, and I did the harness up fully.
At about this point, you may see some interesting reactions - becoming legless creatures is one. And this is the part that we keep short - maybe only a few seconds, depending on the reaction. So for Ava's first experience of the harness, I took it off after only about 30 seconds. She reacted quite calmly to the thing that was around her and needed to be off; a flop on the side, some feet up to hook in and pull it off, and teeth down to also tackle it. She got lots of praise, and that was the end of our session.
The goal in any training is pleasant association, and doing it little and often. So our subsequent sessions have had the time extended in accordance with how Ava's feeling. And I also start to put play into the session. This works to distract the cat from the sensation of something lying on their body, and persuade them that they do actually function while the harness is on! Some cats decide they have no legs, some cats decide they have no balance. Ava was a little bit of both - a tilting cat who wormed along on one side, before 'forgetting' and acting like her normal self because the toy was just so tantalizing. I also include feeding with the harness on, working on the same principle of distraction, and persuasion that all is right, and everything works as normal.
So we are almost at the stage where an outdoor walk can happen. We need a few more walks on the lead inside the house of course, before the outside door opens. And once that happens, walking happens at the cat's pace. Kato was initially fairly hesitant - there were a lot of sounds to be cautious of. His first walks happened around/on the doorstep, and were as long (short) as he wanted them. And this is how we do all of his walks - if he doesnt want to go, he doesn't have to go; if he wants a long walk but hanging out near home, that's what he gets; if he wants to walk further, we go as far as he wants. I'm quite glad that today, he decided he didn't like 10 degrees, with wind and rain, and only stayed out for 15 minutes! Ava meanwhile, greeted us both with a mournful meow because she had been left behind!
I have more information on equipment and the cat-walk experience on the 'equipment & furniture' page - 'outdoors & walking'.