I know there's a bunch of these posts on here already, about things to do to fix your game/make it load faster etc. but some of the things I've tried that have worked I haven't been able to find in this sub, so I thought I'd compile an updated list of things to try.
(Disclaimer: I am in no way a computer expert, just a generally good troubleshooter I'd like to think. None of these were my own ideas, they are things other users recommended, I tried, and they ended up working for me. Most of these require you to edit and delete various files and folders, if you're not confident with messing around in your computers files then I'd recommend backing up [copy pasting to desktop or wherever] any files and folders you're about to edit, in case something goes wrong, or to just give yourself piece of mind.)
These links helped me when I had issues with my computer overheating and crashing the game. They helped when I played a save file for so long that it would take up to 30 minutes (no kidding) to load up, or even save. These links have also helped with general lag ingame.
Just for reference I've got a Gigabyte P35W V3 running a NVIDIA GeForce GTX 860M card. I keep my Sims 3 graphics settings around medium, with texture and sim detail at the highest. I could have them all at maximum if I wanted, but it's a stretch for my laptop.
So first of all I was having issues with the game overheating and crashing, and figured out it was due to the FPS. I also had Vsync in my Nvidia settings turned off. To fix it I first followed [this] (https://www.reddit.com/r/thesims/comments/3z1no3/how_to_enable_vsync_and_other_settings_on_a/?ref=share&ref_source=link) guide. It helped, but didn't completely fix the problem.
I then looked for another fix and remembered that in the past I'd gotten FPSlimiter and 3booter off of the [MATY forums] (http://www.moreawesomethanyou.com/smf/index.php?topic=15585.0). I got it again and my game ran like a dream, my laptop ran much cooler than before. Since that forum isn't very friendly to those seeking troubleshooting tips, I'll also include [this guide] (http://forums.thesims.com/en_US/discussion/843035/3booter-and-fpslimiter-what-they-do-and-where-to-obtain) for FPSLimiter and 3booter. So download the files from MATY, but for actual help, refer to the second link.
Okay next what I did was [increase the amount of RAM The Sims 3 has access to] (http://cloudwalkersims.tumblr.com/post/63397207980/if-you-have-more-than-4-gb-of-ram-you-can-give). The default is 2gb RAM, so if you only have 4gb RAM then DON'T BOTHER with this step, as you should only allow the game to use up to 50% of what you have. If you have 8gb available though you can bump it up to 4gb used, or if you have more like 12gb or 16gb you'd change the amount to 50% of that. I have 8gb available and the game was only using 2gb, by bumping up the amount to 4gb it really helped things load quicker ingame, so for example when I went from Map View straight into a house, the furniture would render quicker. Also found more subtle improvements in gameplay.
Next what I did was create a bat file to automatically delete all the safe cache files. [Here] (http://games4theworld.bestgoo.com/t8126-automatic-sims-3-cache-file-deletion#) and [Here] (http://games4theworld.bestgoo.com/t22999-the-sims-3-optimization-guide#) Read from "Step 6 Deleting Cache Files".
These cache files are safe to delete: CasPartCache.package, compositorCache.package, scriptCache.package, simCompositorCache.package, SocialCache.package, UserPresets.package (OPTIONAL, WILL DELETE STYLES), and any World cache files in your folder.
Follow the directions really carefully in this link, you'll need to change the names in the command to what's relevant to your computer. I copied the command from the "Optimisation Guide" link, and used the other link for further assistance. I'll post the command I use in my bat file below, I've linked the launch address at my "3booter.exe" file instead of straight at "ts3.exe" so that I can just use the bat file as an all in one launch button.
forfiles /p "C:\Users\cswar\Documents\Electronic Arts\The Sims 3" /m *.package /d -1 /c "cmd /c del /q @path"
forfiles /p "C:\Users\cswar\Documents\Electronic Arts\The Sims 3\WorldCaches" /m *.package /d -1 /c "cmd /c del /q @path"
start /d "C:\Program Files (x86)\Electronic Arts\The Sims 3\Game\Bin" 3booter.exe
wmic process where name="TSW.exe" CALL setpriority "realtime"
I'd suggest looking through the rest of Games4TheWorld's Optimization guide for further things to try to fix your game up. In the guide they explain and recommend NRaas mods (which I religiously use), the ones listed there genuinely help your save files from becoming laggy, buggy, and even corrupted in the long run.
Next, I have a large Legacy save file in my game, I'm 5 sim weeks into my town, it's a MASSIVE world, I have 180 human residents (not including service/npcs). I've disabled any pets/stray animals so that they don't get stuck and make my game lag. My save game can bloat up to about 120-130mb at times, which makes loading and saving so excruciating to wait for. Before I found this fix I was saving my game then heading off to make dinner, take a shower, even take my dog for a walk. [This fix] (http://nraas.wikispaces.com/Kuree%27s+Save+Cleaner), explained far better in the link provided, brought my 120mb save file back down to 65mb, and cut my loading/saving time down to 4-6 MINUTES. I mean, for a game that's still a lot, but for the Sims 3 that's REALLY GOOD.
That's all from me, if you require further help or just want to ask me something, comment below and I'll get back to you :)
TLDR thanks to /u/Lydocia
[vsync] (http://www.tomshardware.co.uk/forum/317726-33-question-sync#7122931)
[FPSlimiter and 3booter] (http://www.moreawesomethanyou.com/smf/index.php?topic=15585.0) + [help] (http://forums.thesims.com/en_US/discussion/843035/3booter-and-fpslimiter-what-they-do-and-where-to-obtain)
[increase RAM] (http://cloudwalkersims.tumblr.com/post/63397207980/if-you-have-more-than-4-gb-of-ram-you-can-give)
[bat to delete cache files] (http://games4theworld.bestgoo.com/t22999-the-sims-3-optimization-guide#) + [help] (http://games4theworld.bestgoo.com/t8126-automatic-sims-3-cache-file-deletion#)
[save cleaner] (http://nraas.wikispaces.com/Kuree%27s+Save+Cleaner)
Plus additional tip: [merge custom content] (http://sims3.crinrict.com/en/2011/04/tutorial-combine-package-files-to-reduce-lag.html)