Puggins
Explorer
I can only give you my experience as an example. I would recommend the following for low level casters:
1. Use an ancestry feat to get a weapon. Go a little Gandalf or some other weapon and use it to boost your damage at low level. Every ancestry has weapons as an option so a caster can add some variety to his actions. A weapon attack with a save spell can be quite a nice little damage boost. This should help you get through low level as your slots are low.
2. If you find consumable scrolls with decent spells, blow them off after you add them to your book.
I think these qualify as "out of the box" thinking, but they're definitely legitimate points- spellcasters maybe shouldn't expect to be able to rely on spells constantly throughout an adventure. This thinking was pretty much baked into the rules before 3rd edition.
3. The worm seems to turn around 5th level when you get fireball. Don't use your fireball on single target fights. Blow it off on AoE fights against rooms.
I DEFINITELY disagree here. The turning point is at 7th, when they get expert spell casting and 4th level spells all at once. At 5th and 6th they are so woefully behind martial user in attack bonus and equivalent DC and still predominantly saddled with reflex-oriented spells (which is the strongest save for most low level monsters) that even equivalent level enemies are really difficult to hit.
Reference:
6th level fighter using +1 sword, 19 str -> 6 (level) + 6 (proficiency) + 4 (Str) + 1 (weapon) = +17
6th level paladin using + 1 sword, 19 str -> 6 (level) + 4 (proficiency) + 4 (str) + 1 (weapon) = +15
6th level wizard, 19int -> 6 (level) +2 (proficiency) + 4 (Int) = +12
In terms of effectiveness, paladins have (roughly) the equivalent of advantage from 5e in hitting any given monster compared to the wizard. The fighter has substantially more than that.
4. Try to get a useful focus spell or ability.
5. Remember how things work. Sickened is good because it takes an action to attempt a save to get rid of it. Frightened can be applied multiple ways. Summons creatures can flank and attack. This is adds a little damage while also boosting martial damage. Sickness and frightened lower saves and ACs improving your chance to hit and affect a target. You want to find ways to add a little damage, while shifting ACs and modifiers with spell slots. Those are the spells and abilities you should seek.
The only casters I find wanting at low level are wizards and sorcerers. If I were to build one now, I would build them differently than I did when I first started. I would get a weapon. I would not devalue abilities that applied sickened and frightened. I would cast more often when good opportunities presented themselves. I would better understand how affects synergize like haste with casters. Haste allows a caster to move, cast a 2 action spell, and make a 1 action weapon attack, which in aggregate can add up.
Let's be honest, though- most of the others aren't relying on attack spells to contribute. Don't know if the Oracle or Witch makes this list now either.