First things first, although I am sure you are aware of that: make sure that your system meets the minimum requirements to run Assassin’s Creed 3. Even if it does, try tuning down the visual settings and make sure that you have downloaded the latest drivers for your card (since they usually have performance improvements for top games like Assassin’s Creed 3).
If these still haven’t fixed the game crashes and freezes, here are some more advanced tips regarding what to do:
1. Some users have reported that, strangely, un-updated sound drivers were causing the game to crash. So make sure that you update your sound card drivers, especially Realtek and Creative Labs (for other manufacturers, search on Google)
2. If you have a multicore processor, try disabling them as this might be the problem for the crashes.
3. Many crashes and especially game freezes of Assassin’s Creed 3 are caused by the game asking for too much performance from the computer. So try to disable VSync and multi-sampling to fix these problems.
4. Make sure that you have installed the Day One patch from Ubisoft. The developers are aware of many bugs and crashes and they fix many with the crash fix. Find out more about it on the official forums (SPOILERS, though!)
And right now, this is all I have in terms of tips and tricks on how to fix Assassin’s Creed 3 crashes and freezes. I will do my best to find more solutions for you, so make sure to check back soon – and also let us know in the comment section below about any possible solutions you might have, as well as your problems with the game and maybe somebody will be able to help.