Begin harness training inside so it's a safe, controlled environment. Give treats and praise for wearing the harness.
Make sure harness fits snugly but allows full range of motion. A too-loose harness can slip off.
Engage in playtime while your cat is in the harness so they associate it with fun.
Limit early harness sessions to 5-10 minutes. Cats adjust to harnessing gradually.
Use extra enticing treats like tuna or chicken during training to motivate your cat.
Some cats take weeks to get used to a harness. Keep sessions relaxed, rewarding and consistent.
Verbally praise and reward any steps forward like allowing the harness on or walking in it.