The most important thing is to have small bowls on your tray (preferably with edges). Once you have a few small bowls in place, you can just start piling on snacks.
I like mixing salty with sweet so everyone has a good variety. I also try to include fruit and/or veggies too.
Add in a dip or hummus with crackers, some popcorn, nuts, cheese, and some salami. I like making a salami rose for a really easy way to make it look extra fancy.
Next, add in some fresh elements such as herbs or even decor such as decorative picks.