"The warlock does not cast spells" so I'm a little confused by the question.
Are you talking about that Warlock? Or some other class? Witch Archetype Warlock?
If so, 1st level I'd go mudball (no SR), Sleep (change later, but 1st-3rd level is good), web bolt, and pick another... They don't get grease, so that CC spell is off the list.
LOL. Ok so this is what you are talking about:
Thank god they didn't make more than one type of warlock it's own class...
0 Level spells: Detect Magic, Ray of Frost, Disrupt Undead, Mage hand or acid splash (depend on if you are planning on opening any small doors at range).
1st level: Shocking Grasp, Grease, Vanish (great at CL 2+), and Truestrike. (Vanish, TS, whack with a Cutlass for 18-20 crit range on Shocking Grasp delivered through weapon); sub in expeditious retreat if you want to be able to move fast.
2nd: Invisibility (maybe, if Vanish isn't cutting it for you), Minor image, Glitterdust, Darkness (if you have darkvision). If you think like a magus, you'll put Shocking Grasp with a Reach Spell metamagic added (picked up at level 3 feat) here for a 4-5d6 invisible ranged touch attack(+2, no dex to ac, +3 if metal armor or weapon, BAB +3 +dex bonus (ranged attack) so 2+ most days for 4-5d6 no save). Now you don't even have to worry about Truestrike unless you attack with your weapon.
3rd: Haste, I'd say Keen Edge, but you should be using APP to boost your weapon with this instead of wasting a spell slot. 15-20 crit via Cutlass, yeppers. Vampiric Touch and whatever else you want. It gets trickier from here in out as you will be more selective as to what you want your Magus to do / how you want to control a battlefield.
ps. I love the Tattoo Chamber ability for shoving wands and staves up your sleeve...
What are you wanting to do with your character? You have a spellbook, and full access to the Wizard spell list...so you can really do just about anything you want with it.
If you are wanting to do combat, I would go with buff spells to make yourself stronger/tougher. Mirror Image, Vanish, Invisibility, Shield, Mage Armor, etc.
If you are wanting to hang back and be more of a caster, team buffs and crowd control spells are always nice.
The nice thing about having a spellbook is that you can learn all the spells you want over time, and tailor your choices on a session by session basis as needed.
Mystic Bolt is a pretty terrible ability, it scales horribly...it is barely better than the attack cantrips on its own. The only way I have figured out to make it even somewhat viable is to multi-class into Unchained Rogue and eventually Arcane Trickster, so you can add sneak attack damage with it.
Optimizing Mystic Bolt is a matter of using the TWF chain and Rapid Shot to throw out as many as possible while taking advantage of them being touch attacks to actually hit and grabbing Demon Smith's Gloves for an extra 1d6. This works fine till the mid levels, but then you get crushed by resistances and immunities which you can't counter due to the complete and utter lack of support for mystic bolts. At the very least you need to get your GM to approve use of a Kineticist's Diadem.
This will likely be for War for the Crown, and if the Player's Guide is to be trusted, it's mostly humanoids. At the higher levels, you get additional damage types to help with resistances, as well as the Arcane Striker talent. TWF tree + Rapid Shot is indeed the plan, basically turning me into a magical machine gun. I'm looking at generally buff spells, preferably long duration to compensate for small number of slots. I'm aware it's not a great choice, but I do like the idea of an all-day blasting superhero. If it's really, truly, monk-level awful, then I'll just go do a Kineticist or something.