I've just gotten into DnD, and been running a Paladin (Level 4, Oath of the Crown). As I'm getting used to my abilities, I've found certain fun tactics with which to decide on selecting and using my given spells. Here are some of my favorites and why.

Detect Poison and Disease: I've been loving this one in particular as a Ritual spell, as not only does it give me notice when poisons and diseases are present in the party or NPCs in need of a good five-point shoulder pat, but it allows me to spot some traps early, and gives the party a huge heads up for the creatures we've been fighting, namely Wyverns and Goblin/Hobgoblins with poisoned weapons.

Bless: Just been a good battle spell in general, giving those that are going to be more consistently damaging foes better hit and saves, which is always nice.

I'm playing a Druid right now and it depends on what I think will be the most useful that day.  For example, if I think that the rest of the party is likely to need healing I'll prepare Cure Wounds.  If I think that we're likely to need to be sneaky I'll prepare Pass Without Trace.  If I think that we're likely to be fighting in a 10' to 20' wide corridor I'll prepare Gust of Wind to keep our opponents pushed back away from us.  When I think that I'm going to be in melee a lot and no other Concentration spell will be incredibly useful, I'm playing Circle of the Moon, I prepare Barkskin  The spells that I have prepared varies from day to day.

My biggest caution that I'm always super careful about is Concentration.  Because I can only maintain Concentration on one spell at a time I'm careful to make sure that I have spells prepared that I can use while I'm concentrating on one "big" spell.

As a fellow paladin player I have some bad news...paladin's can't cast spells as rituals unless they have a feat to do so. That said,  I never prepare detect spells and leave it to my party's druid and wizard. Bless is a great spell that I should probably use more often. Shield of Faith is also nice if you're in a bind or if a low AC party member gets surrounded and need some extra defense. Since many paladin spells require concentration, I've also have been trying to use Command more often when I'm already concentrating on a spell and can't get into melee.

Nearly all the paladins I’ve run into hardly ever cast spells at all.  They just save all their spell slots for smiting and leave the spell casting to the full casters (Wizards, Clerics, Druids, Sorcerers and Warlocks).

Yeah, figured that out later. x3 DM was cool about it, though. It was super-confusing, 'cause they were marked as ritual spells for Paladin still on dndbeyond until the recent revamp of the character pages.

80% of the time I spend deciding what to prepare is spent debating whether I want to prepare Tasha's Hideous Laughter, for a more versatile secondary target shut down, or Hold Person for a humanoid-only, primary target I'll-hold-them-you-beat-on-them move.

I try to shy away from damage-focused spells, since there are enough damage dealers in the party, so I try to focus more on control and buff/debuff spells (the barbarian loves my Haste, Ray of Sickness is kinda hard to land (hit AND save), but poisoned is nice to have on enemies).  I always have Shield, Misty Step, and Counterspell prepared, as any self-respecting Wizard should.  Being a Necromancer, Animate Dead never leaves my prepared-spells list.

Man that confused me. I was trying to figure out how a paladin would have access to those spells.

Paladins do have access to Ritual spells, they just can't cast them -as- Rituals unless they take the Feat is all.

In one current campaign as a Paladin, I'm casting spells all the time. Detect Magic being quite popular.

Generally, if I don't know what I'm walking into, I'll try to spread it evenly between damage, utility, and movement.

I'm Oath of the Crown, so when I'm out of reach of something, or if it has enough Acrobatics/Athletics to resist my Shield Shove attempts, I can Command it onto the ground instead. n.n Also Zone of the Truth as an Oath Spell is such fun for when you want to do some questioning. :3

I agree completely about Zone of Truth. I would play a paladin more like an Inquisitor and being able to extract confessions and seeing through falsehoods is a big thematic element of that kind of character.