The absolute best method is with a mallet, preferably one tuned to the size and fundamental frequencies of the bowls you have. If you have a large number of varied sizes and tones having more than one mallet allows you to stay in the range of each related part of your set.
Best Singing Bowls has a sophisticated set of mallets, precision manufactured in the United States. These mallets cover the full range of tones and sizes and allow play with a minimum of the harsh strike quality musicians call “attack”
In terms of laying out your group of bowls, I always prefer to place them in a tone sequence. This way you can choose how to play multiple singing bowls low to high, high to low, or a controlled (or not) in-between mix.