First, the tank should be large, with ample swimming space and hiding spots to prevent territorial aggression. Second, you need to introduce them while the angelfish are young. Young angelfish are more docile and can get used to guppies easier.
Third, you need to provide the fish with enough food. That way, your angelfish won’t be tempted to snack on the guppies. Finally, monitor the tank dynamics regularly and be prepared to separate the guppies if the angelfish start attacking them.