Help with gameplay ideas.

I have my main save where I play rotationally 30+ households. I have no schedule, I just play who I want for how long I want (I pay attention to aging though). My aging settings are long lifespan, active household only, and townies aging when needed. I try to think of a story for each sim and play in a way which suits it. I take a lot of screenies and publish some of the stories in my blog.

I also started a legacy to play more goal oriented. The aging is on normal, for everybody. Neighbourhood strories are on, NAPs are on. I love the challenge of first starting with a household, so I created legacy rules where each generation unlocks a new world (they can visit the previously unlocked worlds, but have to spend a night there). Each gen gets 20k from the household funds when they move to the new world and they must provide that amount to their own child. I remake the world when they move in to suit their needs, for example my next heir is a foodie so there are two restaurants. It's like a legacy that gets reseted each gen.

Edit: Forgot to say that in the legacy I randomise all their traits and aspirations. I try to play as the game tells me to play.

1. Start with a new sim and try one of the Scenarios.

2. Try a new challenge.

3. Pick a career and aspiration you've never done.

Depending on how many packs and extensions you have

Try a challenge
Include more occult sims
Pick traits you've never or rarely used
Try a new career or aspiration
Give your sim your own milestones or life events
Do the not so berry challenge, it seems to shake up game play for many and expands the game play by doing things some of us don't even know about or tend to consider

Have a terrible sim that seeks redemption after getting the atrocious reputation. Aim for pristine. Have a pristine sim that becomes terrible after some life changing event like a divorce.

Challenges tend to help me the most

There's so many things you can try, but also none of them will guarantee that you stay focused over time. Some times the best thing is to take a break from it all.

You could try adding some longer lines into your game. Here's an idea that you can up/down scale as you like:
Create 4 households and give each of them preferences such as one career field they love and one they hate, one color they love and one they hate, a main aspiration they love and another they dislike strongly - and maybe a few more things to focus on like one specie to grow etc. These things won't need to be complicated to add to interesting story lines.

Try to make a few long lasting conflicts between some of them, or perhaps even some deals that were made between their ancestors. Say two and two households are well connected, while two will not have any contact with the other two.

See if there are teens or YA who might fall in love with someone in the wrong family The fun might start when trying to blend two opposite families. Or perhaps 2 kids per family and 1 kid doing everything correct, while the other does it "wrong".

Point of this all would be to end up with a few households that actually have a back story that might affect future generations a bit. You can make it as complex as you like, or perhaps quite simple. Not all mentioned preferences can be registered in game, so you might need to keep some notes, at least for the start.

I really like having different households with different things going on in them and rotating.
Leaning into the weird things the game throws at you, instead of avoiding them, tends to create more funny and fun gameplay imho.
I also like to have a couple of different save games, where one or two saves are more involved stories that I can be really creative with long-term, and one or two saves are just relaxing and watching my sims go about their lives day to day.

Oh, and try some of the traits you don't use very often, if there are any. Some of the annoying ones (kleptomaniac, evil) can actually be super fun if you lean into them and use them in gameplay rather than trying to minimize their effect on your game.

Try to "Play Vanilla". Without using ANY cheats or MODS, it will give your Sims a real challenge. Try to make a legacy generation where your family tree has lots of people, and it'll make you feel like you're a... Well I can say, the king of tree....

I don’t like to play goal based challenges, so generally when a sim’s story ends, I have to wait for inspiration to start a new one. My current save is my longest Sims 4 save, yet. The difference is that I’m playing a whole imaginary world that takes place in our sims worlds. When one part of the story goes stale, I can always find another character that interests me. I tend to bounce around a bit, but it keeps my game from becoming repetitive.

I have a set idea, but sometimes I just kind of wing it. I pretty much own all of Sims 4 for a console, with just the base game on a PC.
I have multiple save files, with different things going on to keep my interest.
For example my somewhat planned ideas are things like Frozen or Harry Potter. Some families I keep as canon as I can, others would be semi-canon, or AU. I throw some gender bends in as well. It keeps me entertained, because you see a variation of the same Sim running around.
Another save file, I recreated the Sims I created in Sims 2 in the Sims 4.
A couple other save files I have a mixture of Sims I created, and ones I downloaded.
I am also playing a challenge for a save file.
I have so many families, and choose the one I want to play at that moment. Some of my Sims get more attention than others.
Finally, I tend to focus on a family to further their careers, or play off the grid. I have one family that lives just on a lot, and it is a father and two teen sons. They all work, and the plan is to slowly give them more rooms when they get enough money.
Also, if you find yourself making the same families, switch the dynamic a bit. In some families, I have the typical mom/dad and kids, single sims, and some that have grandparents, the parents, kids, and maybe a sibling to one of the parents.
If you are bored with giving the Sims the same look, try going to the Gallery, and download some Sims, and mix genetics. I got some really unique looks for Sims that I wouldn't give them by doing this.

I really enjoy the scenarios for giving me abit of inspirations of what to play.
Also 'pick a pack!'. I find that I often tend to ignore the gameplay in some packs so if Im bored I decide on a pack and immerse myself in the gameplay. So throw myself into university life, aim to be the best spellcaster, become a selfsufficient farmer, etc.
or I just Google challenges and copy somebodies elses good ideas!LOL

Have you ever tried playing a household based on a different timeline like Medieval or 1920s or 1970s or even Sifi Future?