The key to walking or coming and taking the pet outside is taking the time with the pet. You don't want to rush it and stress the pet. Taking the extra time to spend with your pet will build a rapport over time and a trust will be built up. If just taking them outside I like to play with them some to burn off a little energy. If walking it's good to let them feel unrushed but at the same time getting them the activity that they need. When leaving let them know how well they've done and you'll see them soon. That leaves them on a positive note and makes the next visits less stressful and enjoyable for the myself and the pet.