Heuristics are basically Rules of Thumb. While there is really no substitute for User Testing to find out if your sites are elegantly effortless for your audience, you can at least start somewhere, using well-established guidelines to assist in the process.

There is no better place to start than with Jakob Nielson:

Usability Heuristics

1. Visibility of system status
Example:
Hourglass
Blue bar creeping across its box showing how much time is left to complete a process
"Your order has been received" page
"Breadcrumbs"
Rollover buttons

2. Match between system and the real world
Example:
File-folder tabs for navigation
Buttons which act pushed when you click on them
Simple language on labels, for example "product code" instead of "item SKU" (unless the site is internal, and SKU is the more common term)

3. User control and freedom
Example:
"Undo" button
Stop button on browser
"Remove from cart"
Close window
Unplug the machine

4. Consistency and standards
Example:
Don't (as I have done) call something "Help Files" in one place and "Tips and Tricks" in another.
Use what people know: put navigation on the left, links to special site tools on the upper right, and featured items on the right.
Especially if you use unconventional navigation, your site should make it easy to learn the new way (see Rule 3) then reinforce the learning through strict consistency.

5. Error prevention
Example:
"Are you sure?" message
Validation - check for @ sign in e-mail addresses
Clear labels - "Check Out NOW."
Large enough buttons

6. Recognition rather than recall
Example:
Choose from list of options
Mouse-over tool tips
Help system always available

7. Flexibility and efficiency of use
Example:
Different methods for novice and expert - mouse vs keyboard
Frequently-used actions become first choice - on Mapquest, the addresses you've looked up show up as "Recent Searches" the next time.

8. Aesthetic and minimalist design
Example:
Omit unnecessary words
Leave clutter off the pages, and that adorable animated gif you think is so cool. Cute once, annoying forever.
Japanese study found that beautiful things were actually easier to use. Experiment repeated in Israel, with the same results, completely contrary to expectation!

9. Help users recognize, diagnose, and recover from errors
Example:
Useful error messages - "Incorrect Password. Check to see if your caps lock key is on."
On Google - "Did you mean web site?" when you typed web site.

10. Help and documentation
Example:
Your site should be designed so well that documentation is not necessary.
If not, documentation and help should be readily available, clear, and correct.
Popup help
Clear link to customer service


More Info: http://www.useit.com/papers/heuristic/heuristic_list.html