Before delving into how you should build a relationship with a deity, one must first find a deity with whom they wish to form a union with. Before choosing one indefinitely, you should always check for the possibility that a deity is trying to reach out to you through subtle signs in nature. Sometimes a deity likes to be the first to initiate contact, but they cant just openly convey this desire plain for the world to see--at least not without the potential repercussions.
An example of deity contact would be seeing peacocks or finding their feathers in areas where you normally wouldn't. This could relate to the Goddess Hera because of her association with the sacred animal.
If you don't see any signs despite your efforts, don't worry, most people won't. Sometimes you must be the first to initiate contact. If you feel lost about who to choose, just find a deity that you feel most connected with--be it because of their domain or origin.
Once you've found a God/Goddess, the best thing to do is to make yourself known. This helps lay the foundation for future interactions. After you've introduced yourself, you should leave an offering or recite a prayer as a sign of respect. Just be sure to leave a meaningful offering related to their domain if you plan to give one. From there, you must take time to build your relationship. A bonded union doesn't happen in a day. To build a connection you can:
If you do not wish for a patron, then that is also fine. You can simply call a deity as you need them for your magickal workings and then leave them something in return. If you wish to focus on Love one minute, you could invoke a goddess like Hathor, Freya or Aphrodite. If you then wish to focus on attaining wisdom, you could invoke a deity like Thoth, Odin or Athena. Always be sure to leave an offering if you do this, because they do not need to lend you their energy for spells and rituals. This is out of their own free will.
If you don't know an appropriate offering to give, this is a basic list of three to get to get you started. One can also honor and work with more than one deity since jealously is not a valid concern among the Gods but be sure you're up for it first. Most of these offerings are either offhand knowledge or based on common herb associations.
Zeus/Jupiter (God of the skies): oak, olive, pine
Poseidon/Neptune (God of the sea): pine, ash, fig
Hades/Pluto (God of the underworld): cypress, mint, pomegranate
Apollo (God of the sun, music): heliotrope, hyacinth, frankincense
Artemis/Diana (Goddess of the moon, wildlife): silver fir, birch, hazel
Ares/Mars (God of war): buttercup, ash, aloe
Athena/Minerva (Goddess of wisdom, war strategy): olive, apple, mulberry
Aphrodite/Venus (Goddess of love): olive, cinnamon, daisy
Ra (God of the sun): acacia, frankincense, myrrh
Osiris (God of the underworld): acacia, grape, ivy
Isis (Goddess of marriage, fertility): fig, heather, wheat
Hathor (Goddess of love): grape, rose, mandrake
Horus (God of the sky): horehound, lotus, persea
Bastet (Goddess of cats, music): catnip, vervain, mint
Sekhmet (Goddess of war): cinnamon, ginger, blackberry
Anubis (God of funerary): frankincense, mistletoe, parsley
Odin (God of wisdom): mistletoe, elm, ash
Freya (Goddess of love): strawberry, daisy, primrose
Thor (God of thunder): thistle, houseleek, vervain
Loki (God of trickery): cinnamon, dragons blood, alder
Baldur (God of light, purity): st. johns wort, daisy, myrrh
Tyr (God of war): thistle, ginger, high john root
Hel (Goddess of the underworld): cypress, elder, ivy
Bragi (God of poetry, music): almond, apple, iris
Ana/Danu (Goddess of nature, fae): bay, patchouli, ash
Dagda (God of fertility, knowledge): oak, ginseng, rowan
Aengus/Angus (God of love): sandalwood, periwinkle, vanilla
Lugus/Lugh (God of the sun): sunflower, cedar, citrus
Morrigan (Goddess of fate): mugwort, sage, jasmine
Brigid (Goddess of healing): blackberry, eucalyptus, chamomile
Belenus (God of light): frankincense, cedar, heliotrope
Camulos (God of war): cedar, acorn, aloe
Once you believe you have attained a steady bond; you may take a chance at invoking your deity. I personally recommend using sigils. This can be done by spelling out a deity's name and removing any present vowels or repeating consonants. The remaining letters are then turned into a symbol of your own design but doing this is not a necessity. Nothing is guaranteed in invocation. Some practitioners claim to have caught a glimpse of their deity's true form while others claim to have heard a voice echo in their mind. This is a subjective experience, but one shouldn't expect a full materialization to occur and magically vanish hardship. I hope this explanation proves useful, and be sure to have a blessed day!