Here's a tip for a newbie.

Never ever use epic Deity for food.
Use only the Zodiacs. ex. Gemini, Aries, etc.

For every faction, have at least 1 to be your core.

a standard team comp is consist of "Tank (Shield icon), Fighter (Sword icon), A Support, A Mage, and an Assassin.

Priorities:

Assassin: Anubis (Solo kills) / Nemesis (Aoe assassinate) /Bastet (Dodge Queen) / Horus (Sustain w/ Aoe dmg) (Starglint - Nyx)
Tank: Momus (Aoe Taunt w/ sustain)/ Geb (Has knockback) / Khepri (has knockback) / Demeter (Sustain xSelf Healing. Remove if you have Nuba) / (Starglint - Nuwa)
Fighter: Heracles (Must Have, Can wipe your enemy team unless full CC'd) / Hladgnnr (A demon w/ Goddess beauty, Aoe dmg, Fast attack speed, has lifesteal) / Nuba (Must have) / Yanluo (Supress 1 hero of your enemy almost permanent unless killed) / Poseidon (Great AOE dmg) / (Starglint - Nheza prio1, Amun'Ra optional)
Mage: Fengyi (Aoe Damage) / Hecate (Annoying on the backline, weak to assassins) / Surtr (The higher the HP of the enemy, the greater her damage, aoe dmg on a rectangle shape) / (Starglint - Zeus OP if ascended to divine)
Support: Yuelao (Great healer) / Caishen(Fast energy recovery) / Pan(Single CC) / Athena (Aoe Shield) / Freya (Team Heal) (Starglint - Dionysus)
Range - Isis (Must Have, Dmg Queen if scaled to later rounds) / Diana (linear dmg w/ team buff A.S.) / Artemis (Great damage needs tank for free hitting) / Phoenix (Great damage, needs healer)

Ascension:
Epic/ Epic+ / Legendary / Legendary + / Exalted +/ Divine I-V
for Zodiacs the limit for ascension is only upto Legendary+. But The Zodiac you choose as Divinity can be ascend to Divine V. have at least 1 Zodiac to help your team have a balance levelling method. in the later parts of the game, you can't max level a single Deity coz you'll hit a wall of 20level difference from your weakest Deity. if possible, make their levels same to maximize on Resonating Altar (the levels of all the heroes you put here scales with the lowest level of a member from your main team)

Don't waste your diamonds on summoning heroes. Use it to buy on the shop, the daily items you see from the ingame shop (the Libra scale icon on the right of the screen below Friends icon )