The Sims 3 isn't bad right out of the box, but the modding community has come up with some mods that make it quite a bit better. This isn't a full list and I'll likely add more to this post in the future.
I highly recommend the Nraas Industries series of mods. They work in conjunction with each other and make it easy to manage your came and customize it to your liking.
The ones I use:
Relativity :If I were to only use one mod, this would be it. It allows you to control how many game hours go by in one real time hour. I found that the vanilla time went by far too fast and there wasn't enough time to do anything. The time scale can be set to whatever you like, making it far easier for Sims to live their lives.
Returner : A huge list of settings to help control Sim behavior. I use it for things like making sure that Sims eat their leftover food before making more, regularly clean out the fridge, shorter nap times from 120 minutes to 30, etc.
A List of Retuner's Available Settings
Story Progression and Woohooer : Something about the Sims that I did NOT like is that the game seems to have Sims set up to cheat on each other. The game does not take each characters' traits into account and instead makes them do what it (the game) thinks the neighborhood wants. These mods have settings to make sure that married Sims are faithful to each other. In fact I read a post where a user was complaining that an aunt was flirting with her nephew (yikes). With these two mods I'm able to play in a far more wholesome neighborhood.
A List of Story Progression Settings
Decensor : Removes the square mosaic that comes up over Sims and pets when the characters are bathing or relieving themselves.
Overwatch : This mod can be used to export and import the settings of the other Nraas mods so you don't have to go through and reset everything anytime you start a new game.
Master Controller : Basically it makes it far easier to use cheat codes. You can easily edit your characters' appearances, give your household money, adjust skill levels, etc. Not to mention dealing with the occasional glitch that can happen no matter how well a game is set up.
Another mod I recommend for making sure that Sims behave themselves is No Auto Smartphone Tasks.
I quickly became annoyed with the cell phone feature. My Sims were constantly pulling out their phones to stream videos, to text, and take pictures. What was even worse is that the auto-phone behavior contributes to the above mentioned "cheating problem". In the afternoons I would send Neldor to one of the parks to play his guitar for tips to help with the bills. Occasionally he gets hit on by female admirers. That in itself isn't so bad and is to be expected, but that brief interaction would cause him to know the phone numbers of his admirers and he was constantly pulling out his phone to call them!
[Those who are familiar with Neldor are likely having the same reaction that I did: Never in a billion years would Neldor do this.]
With the no auto-phone mod, my characters don't do anything with their phone unless I tell them to. So no more of Neldor trying to make calls that the character would never ever make. The same goes for Aeronwen.
Opportunity Phone Fix Override : Being freelancers, Neldor and Aeronwen like it when they get offers from town to go teach an art class, or play music for a school assembly, etc. This mod fixes the glitch that is caused when the Into the Future DLC is installed.
Tail Thickness Slider for All Pets because in the vanilla game it's not possible to give your horse, cat, or dog a nice thick/fluffy tail.
No more shiny horses : Because vanilla horses shine like an automobile. Yes, in real life you can brush a horse until he/she shines, but not so much that there are reflections in their hides.
Default Horse Eyes : Makes horse eyes look far more realistic and alive instead of being a flat black.
No autonomous gaming : The name sums it up. Without this mod they won't practice their writing or get any chores done. They just game.
These aren't the only mods I use, but this is more or less the core of my set up. Those will probably be added to this list later.
Update: 12/14/2023
Register a NRaas mod that altars role assignment for game. What I like about it is that is has a setting remove the Paparazzi who follow Celebrity Sims around.
A good place to start when it comes to adjusting the many settings in the NRaas mods is Pleasant Sims NRaas Mod Settings.
Another blog where one can view possible NRaas settings is Sarah Sims NRaas Settings.
Edited to add: Here are some camera enhancements which aid in taking screenshots.
No Camera Fade for Sims
No Drift/Lower Level Live Camera Mod
No Drift/Lower Level Free Cam Camera Mod
I highly recommend the Nraas Industries series of mods. They work in conjunction with each other and make it easy to manage your came and customize it to your liking.
The ones I use:
Relativity :If I were to only use one mod, this would be it. It allows you to control how many game hours go by in one real time hour. I found that the vanilla time went by far too fast and there wasn't enough time to do anything. The time scale can be set to whatever you like, making it far easier for Sims to live their lives.
Returner : A huge list of settings to help control Sim behavior. I use it for things like making sure that Sims eat their leftover food before making more, regularly clean out the fridge, shorter nap times from 120 minutes to 30, etc.
A List of Retuner's Available Settings
Story Progression and Woohooer : Something about the Sims that I did NOT like is that the game seems to have Sims set up to cheat on each other. The game does not take each characters' traits into account and instead makes them do what it (the game) thinks the neighborhood wants. These mods have settings to make sure that married Sims are faithful to each other. In fact I read a post where a user was complaining that an aunt was flirting with her nephew (yikes). With these two mods I'm able to play in a far more wholesome neighborhood.
A List of Story Progression Settings
Decensor : Removes the square mosaic that comes up over Sims and pets when the characters are bathing or relieving themselves.
Overwatch : This mod can be used to export and import the settings of the other Nraas mods so you don't have to go through and reset everything anytime you start a new game.
Master Controller : Basically it makes it far easier to use cheat codes. You can easily edit your characters' appearances, give your household money, adjust skill levels, etc. Not to mention dealing with the occasional glitch that can happen no matter how well a game is set up.
Another mod I recommend for making sure that Sims behave themselves is No Auto Smartphone Tasks.
I quickly became annoyed with the cell phone feature. My Sims were constantly pulling out their phones to stream videos, to text, and take pictures. What was even worse is that the auto-phone behavior contributes to the above mentioned "cheating problem". In the afternoons I would send Neldor to one of the parks to play his guitar for tips to help with the bills. Occasionally he gets hit on by female admirers. That in itself isn't so bad and is to be expected, but that brief interaction would cause him to know the phone numbers of his admirers and he was constantly pulling out his phone to call them!
[Those who are familiar with Neldor are likely having the same reaction that I did: Never in a billion years would Neldor do this.]
With the no auto-phone mod, my characters don't do anything with their phone unless I tell them to. So no more of Neldor trying to make calls that the character would never ever make. The same goes for Aeronwen.
Opportunity Phone Fix Override : Being freelancers, Neldor and Aeronwen like it when they get offers from town to go teach an art class, or play music for a school assembly, etc. This mod fixes the glitch that is caused when the Into the Future DLC is installed.
Tail Thickness Slider for All Pets because in the vanilla game it's not possible to give your horse, cat, or dog a nice thick/fluffy tail.
No more shiny horses : Because vanilla horses shine like an automobile. Yes, in real life you can brush a horse until he/she shines, but not so much that there are reflections in their hides.
Default Horse Eyes : Makes horse eyes look far more realistic and alive instead of being a flat black.
No autonomous gaming : The name sums it up. Without this mod they won't practice their writing or get any chores done. They just game.
These aren't the only mods I use, but this is more or less the core of my set up. Those will probably be added to this list later.
Update: 12/14/2023
Register a NRaas mod that altars role assignment for game. What I like about it is that is has a setting remove the Paparazzi who follow Celebrity Sims around.
A good place to start when it comes to adjusting the many settings in the NRaas mods is Pleasant Sims NRaas Mod Settings.
Another blog where one can view possible NRaas settings is Sarah Sims NRaas Settings.
Edited to add: Here are some camera enhancements which aid in taking screenshots.
No Camera Fade for Sims
No Drift/Lower Level Live Camera Mod
No Drift/Lower Level Free Cam Camera Mod