Often times one of the simplest ways you can positively impact the life of a veteran around you is to simply ask how they are doing.
Listen when a veteran needs to talk. You don't need to feel pressured to respond, just be an open ear.
Reach out to veterans around you. There doesn't need to be a reason - reach out. Invite an old friend, your neighbor, or a new acquaintance for coffee. Be there. Sometimes all it takes is knowing there is someone who cares.