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HOW TO FIX THE SIMS 3 AND (hopefully) RUN IT WITH LESS OR NO LAG - A THREAD:
The Sims 3 is an amazing game, but it needs some help to adapt on modern hardware. There's a bunch of fixes out there that can help with that, and I want to share what I've used. Most of them are probably well known, but I thought I'd put them here so they are easier to find.
If you install the game from Origin, it will be updated to version 1.69 already. If it’s from CD, you’ll need to update the base game yourself to version 1.67 BEFORE you install any packs. You can download the Superpatch for CD version from here: https://simsvip.com/2014/01/24/sims-3-game-update-1-67-12414/
The first fix is 4GB patch, using CFF Explorer (3rd download link: https://ntcore.com/?page_id=388 ). Origin version DOES NOT require this. You need to run this program as Administrator and open TS3W.exe which is located in C:\\Program Files (x86)\\Electronic Arts\\The Sims 3\\Game\\Bin.
Once TS3W is open in CFF Explorer, click on File Header and in Characteristics on the right, click “Click here”. In the next window, check the box “App can handle >2GB address space. Click OK, save the changes and you’re done!
Your game needs to recognize your graphics card. @realjessamica92 has a tutorial on that (). Graphics rules file can be found in the same place as TS3W.exe. If your game is from Origin, then it is in C:\\Program Files (x86)\\Origin Games\\The Sims 3\\Game\\Bin.
Routing issues in vanilla worlds are the biggest cause of lag. Ellacharmed on MTS ( https://modthesims.info/m/1515002 ) fixed most of them. They will replace EA ones in their default locations. Installation instructions are on download pages. Please note that only NEW saves will be affected.
TS3 doesn’t have a framerate limiter, so it puts more strain on the graphics card than needed. Nvidia Control Panel can help with that. I own an Nvidia card, but other cards might have a similar procedure. You can open Nvidia Control Panel by right-clicking on your desktop.
What would The Sims 3 be without Nraas mods? I don’t know because I don’t play without them. The important ones are Master Controller, ErrorTrap and Overwatch. Story Progression is not necessary, but it beats EA’s one for sure. You can find them here: https://www.nraas.net/community/Mods-List
Yet another fix that seems to help is disabling bloom effect. So disabling it can lower lag a bit. This is the shine on objects that appears when Advanced Rendering is enabled. Here’s a tutorial on it: https://annythingsims.tumblr.com/post/104662906911/the-sims-3-removing-bloom-effect
Thanks to @virgosimmeryt, I’ve discovered Razer Game Booster, which optimized the PC during gameplay so that there are less things taking up resources. It can be found here and might help with other games as well: https://www.razer.com/cortex/boost
In Task Manager go to Details tab, find TS3/W.exe while it is running, right-click to set priority to High (NOT Real Time!). Set affinity, and you’ll see CPU1,2 etc. I have eight so I uncheck the last four. Make sure at least two are checked. Repeat this every time the game runs.
Disable all online features in-game and log out of your Sims 3 account if you’re not using it. There are some Nvidia settings that you can tweak as well, below is a screenshot of mine. That’s everything I did (I think) that made my game run with no lag. Hope it helps someone.
If you use Store content, here's also a guide for installing the ENTIRE Store in a little less messy way. It looks super complicated at first, but it's actually really simple and you'll know where your Store stuff is if you ever need to reinstall/fix it: https://forums.thesims.com/en_US/discussion/866577/how-to-install-store-items
Where is the edit button??? This is the actual screenshot of the settings, the one up there was posted twice 
