Super weak for a 1st level spell, primarily for action-economy reasons as detailed in other answers which I won't repeat. Definitely go read them.
Compare Zephyr Strike (XGE) for a 1st level spell that gives advantage on a future attack. It has to be a Weapon attack (so not usable for boosting a high-level spell's chances), and is Ranger only, but is otherwise vastly better than True Strike. You choose which attack, and it does extra force damage (1d8). And is only a bonus action and has other benefits.
1st-level transmutation
Casting Time: 1 bonus action
Range: Self
Components: V
Duration: Concentration, up to 1 minuteYou move like the wind. Until the spell ends, your movement doesn't provoke opportunity attacks.
Once before the spell ends, you can give yourself advantage on one weapon attack roll on your turn. That attack deals an extra 1d8 force damage on a hit. Whether you hit or miss, your walking speed increases by 30 feet until the end of that turn.
Classes: Ranger
Being limited to Ranger-only lets it be stronger, but still this is the kind of power that would be appropriate for a 1st-level spell. It's the same sort of mechanic as spells like Searing Smite, except with those you concentrate until you actually hit.
Note that it is still concentration, otherwise could be combined with concentration spells.
An any-class version of this could still be a bonus action, so you could Cantrip + True Strike on one turn, then benefit from it on the next turn. But that might be overpowered for high-level casters; I don't recommend actually doing that. If you want to try adjustments like that, you're on your own as far as balancing that homebrew.
Keep in mind that 18th level wizards can take a 1st and 2nd level spell to be cast at-will, via the "spell mastery" class feature. A first-level spell that gives advantage on attacks including cantrips could boost their no-resource damage significantly against high AC targets. Of course, so would 2nd-level Flaming Sphere (to use your bonus action on later turns) + Cantrip, or spamming 2nd-level Shatter on multiple targets, if they used their 2nd-level spell mastery for damage instead of 1st.
But with a spell slot, a high-level wizard could cast Bigby's Hand or similar to give them something very useful to do with their bonus action every round instead of this spell.
Other classes with access to a homebrew 1st-level True Strike will have their own balance considerations. This point about wizards should be enough to make it clear that balance is non-trivial. The fact that True Strike is such garbage most of the time might be a sign that the designers couldn't find a way to make it stronger without making it too strong for some cases.