I have a character that would be great for a gestalt combination of Warlock (Pact of the Chain) and Bard (College of Lore), but I have little to no experience building a gestalt class. Can anyone help? What would be the most optimal build for something like this?

Guessing you got the idea from the recent WebDm video. Here's the link to the wiki that they referenced Gestalt (5e Variant Rules). 

Could you clarify what it is you need help on? One benefit of convenience with Gestalt characters, assuming you stick with the same two classes throughout progression, is that you never have to worry about "build" in the traditional sense of taking X levels of one class and Y levels of another. Gestalt with two spellcasters plus Invocations also gives you so many different options to choose from that there is no one optimal build, let alone that optimal for you may not be optimal for someone else.

I think we also need to know a little more about what you want to do with the class, and we don't yet know what your Warlock Patron is unless you are asking for advice there. Being a Lore Bard implies you are a knowledge seeker with extra spells and skills, but you add a little bit of defense/protection with Cutting Words. If you want to expand on that theme then The Great Old One fits pretty well, and you can even choose Pact of the Tome instead of Chain for even more knowledge and spells.

You can become a very effective healer/defender if your patron is the Celestial or Undying, take the Gift of the Ever-Living Ones Invocation for self-healing, use Magical Secrets for more Cleric/Paladin spells, etc. Again, all depends on what you want to be able to do with the class, and you have way more options available to you than just these two.

If you are instead asking for help on the Gestalt rules themselves, here are the basics for a level 1 Gestalt Bard/Warlock:

• Hit Die: d8 
• Proficiency Bonus: +2
• Skill Proficiencies: Choose any three.
• Armor: Light
• Weapons: Simple weapons, hand crossbows, longswords, rapiers, shortswords
• Tools: Three musical instruments of your choice
• Saving Throws: Dexterity, Wisdom, Charisma
• Starting Wealth: 200 gp
• Class Features: Spellcasting, Bardic Inspiration (d6), Otherworldly Patron, Pact Magic
• Spell Slots (total between classes): Three 1st-level spell slots
• Spells Known: Two Bard cantrips, Two Warlock cantrips, Four 1st-level Bard spells, Two 1st-level Warlock spells. Your Warlock Patron may grant you bonus cantrips.

I suppose I should clarify more.

I chose the Archfey patron. The bard's clan has a long tradition of serving this Archfey in secret, trading information to him in exchange for true stories never before heard in the Forgotten Realms, with the magic as an added benefit. Their insatiable thirst for new stories and knowledge suits the Archfey well, as it his chiefest desire to become all-knowing.

Pact of the Chain is more of a thematic choice, since he's on a MacGuffin hunt for a magic book with clan significance and it might undermine that if already has one.

The character himself is a Tabaxi with the Urchin background, and is meant to be a sort of support-trickster and Face in overall function, like buffing the party and disabling enemies with magic while the others go in for the kill, being diplomatic, and some Rogue-like abilities like scouting and infiltration--which I imagine the right selection of spells and proficiencies could help with. What would you suggest for something like that?

And I did need help with the actual rules, so thank you.

Okay, I think I got it set up. Thanks, y'all!