The most common tip – familiarise your cat with the carrier – has never worked for us. Our pets will play in and on the carrier but the second we plan a trip to the vet, they vanish like small furry ghosts.
Still, as all cats are different, you can try it. Most importantly, layer it with a thick absorbent newspaper in case of bathroom accidents, and top with a comfy towel that has their own scent on it.
On the way there, keep the car cool but not cold, and make sure it's quiet. Leave interested bystanders looking for excursions at home. Don't blast music. Talk reassuringly. Expect the cats to sing opera.
When you're at the vet, act calm, confident and help them avoid being traumatised by cupping their face so they cannot see the needle. Then rub their ears so they're distracted as it goes in.
Afterwards, apologise profusely and break out treats for the kitties and chocolates and a large cup of tea for you.