So i'm not the most paranoid person in the world, but i like to make sure that i'm safe at all times when using my computer regardless of what OS i'm using. To begin with, i have one login on all my machines, with a homemade password that uses at least one capital, number, symbol etc and is at least 16 characters.
(Made a primary code for passwords based on a series of numbers and equations related to the item or website i'm logging into. I don't need to remember any passwords, just the code i created and the name of the place i'm logging into. The correct password is the solution followed by a series of digits and symbols)
If your not sure on what to set for your passwords, or how to make your own little code, check out this Strong Password Generator make sure to read some of the guidelines to get an understanding of how important it is to set strong non-dictionary passwords.
Next i make sure that all my external HDDs are encrypted using a minimum of AES-Twofish encryption. You can use a variety of programs across each platform to create high level encryptions, the most popular appears to be TrueCrypt, open-source disk encryption software for win/mac/linux. It's up to you if you want to create hidden partitions and how you want to mount the drives.
I'm not going to share what partition setups, encryptions, browsers and software i use, rather just point you in the right direction.
Once you have encrypted your HDDs, look at securing some of those pesky incoming connections... A highly recommended connection monitor would be LittleSnitch It may also be a good idea to enable the firewall and enter stealth mode if using OSX. (Always you make sure you select the lock on OSX to prevent further changes from being made [note: also prevents outsider changes without your strong login/master password] )
Many use Chrome as their default browser now, perhaps consider looking at the Tor Project for maximum security. I also always carry a USB with Tails installed on my keys (never know when your going to need to check some important files or emails on someone else's unsecured computer)
Some other things to look into is running an installation of Linux on your computer, some people prefer more compact versions that can be installed on datasticks and leave no trace on the computer of it ever being there after shutting down, such as PuppyLinux when set up to install on the users RAM (Also carry a copy of this on my live USB on my keys). A mini computer in your pocket essentially with all your files.
Also check out the latest release of Ubuntu. LXDE and XFCE versions are available in the form of Lubuntu and Xubuntu. All are open-source and open to donations rather than charging the user. You can dual boot any of these or clean install
http://unetbootin.sourceforge.net/
http://www.intowindows.com/winusb-maker-utility-to-create-backup-and-restore-bootable-usb/
http://www.pendrivelinux.com/