crunchy vegetables–celery, radish, red onion are a great trio
something zingy–pickled jalapenos are great
Dice the chicken and veggies quite small. The ratio of chicken to veggies should be somewhere between 2/3 and 1/2 chicken. Add pepper and mayonnaise and mix so it's wet but not drenched. Start slow, but the flavor blossoms when you reach sufficient mayo.