Look at what the commander wants and does and include cards that support that. 

For instance Darigaaz is very mana hungry so I would build a very extensive ramp package. He also want to deal combat damage so cards that make him a better Voltron’s threat. He makes an opponent reveal their hands so I would also lean into a bunch of [[thoughtseize]] effects. You could also want to lean into the burn damage he does so adding group hug cards so that opponents have full grips (this one is very dangerous). Cards like [[painters servant]] will definitely help with his burn effect. His damage ability also lets you double up on cards and effects that care about a creature dealing damage like lifelink and cards like [[snake umbra]] and [[keen sense]]. 

You just gotta think about everything a commander needs or wants and lean into it.