The pattern of the dying god is one. Although the deities are usually not related, there's almost always a dying-rising god. Odin in the North, Dionysos in Greece, and Osiris in Egypt.
There are also linguistic connections. Proto-Indo-European Dyew Ph-ter "sky father" is the origin of many gods such as Jupiter (from Diovis Pater), Zeus, Tiwaz (commonly known as Tyr), Dagda and Dyaus Pitar. Other linguistic connections include Freyja and Prajaapati, Thor, Taranis, Perun (?) and Indra, Ymir and Yama, and possibly Borr or Buri and Brahman. Keep in mind this is all theoretical.
Deities which aren't linguistically related may still have common origin, but were given different names and titles. Odin is a psychopomp deity associated with magic and trade, so is Hermes. Dionysus is a fertility god associated with trees and drink, so are Thor and Indra. Vulcan is a blacksmith associated with fire and possibly lightning, while Thor is a fire and lightning god associated with crafts. Many earth goddesses are very similar but their titles and names seem to simply be the native word for "earth" (Gaia, Jord, Tellus/Terra Mater, etc.) Keep in mind this is hypothetical.
Symbolism is also common. The Aegishjalmur in the Germanic Culture is strikingly similar to the Indian Asthanga Yantra. The cosmological symbolism of trees is common among Proto-Indo-European cultures (excluding Greece and Rome).