No AV software provides full protection and tends to give a false impression of safety, not saying don't have one but it's all about layering your security.
For basics I'd recommend running as a limited user account (create separate admin profile) with UAC max to start to limit the damage malware can do and to help prevent any executables running without your express approval.
Get an AV of your choice. MSE is decent and free. I use Norton IS 2013 myself mainly due to it's extremely low resource usage and good protection for an AV suite.
Install some on demand scanners like Malwarebytes, Hitman Pro or SuperAntiSpyware and run periodically as you see fit to provide a second opinion.
Keep everything updated, Secunia PSI can do it for you automatically. Also delete any unused programs, limit your attack surface.
If you anticipate issues with removable media then you can disable autoplay to prevent infected USB sticks and the like from running immediately.
Change you default DNS provider to either Norton Connectsafe or OpenDNS as they will filter a lot of malware hosting pages and phishing sites before they even hit your computer.
If you really want to harden the core system further you can do some other things but they can require some trouble shooting to get working smoothly so proceed with caution if at all.
If you're running a 'Pro' version of Windows you can consider running a Software Restriction Policy. This is an incredibly powerful tool with zero performance hit but as above can require some tweaking.
Download EMET and enable all mitigations and work back if it causes issues. Can help prevent against zero day issues and other vulnerabilities.
Guides for SRP and EMET are here
http://www.mechbgon.com/build/security2.html along with lots of other useful tips.
Hope this helps.