Yes, worship is for God alone, but the best place God's light is manifested is in the person of His Messengers.
The Messengers are like the Lamp, and God is like the light within the Lamp. So, when we worship God, we worship the Light within the Lamp. We don't worship the individuality and physical body of the Messengers, but we worship the God, who manifested within them. It is only for this reason, they bowed to Adam, or Joseph.
Prayer, is not always an act of worship though. It is talking and communicating. It is asking for help and confirmation. But some prayers include worshiping.
When we want to talk to God or worship God, we would have to imagine we are talking to a person. This is not the reality though, because God is not a person as we imagine. He is Not like any of His creatures, and has no similarities to them!!!
So, the best way, is to talk and pray to His messengers as they are actually Persons, reflecting the Will and attributes of God to the world.