Several articles have appeared recently touting a concept known as contingency design. In a nutshell, this consists of providing assistance when your visitors do the unexpected or the blatantly wrong thing. This adds an extra level of professionalism to your site, which can lead to more return visitors (or in the case of an e-commerce site, more sales).

Some examples of contingency design are described below.

Error pages: 404 error - This is one of the most important contingencies to cover. It is wise to spend a lot of time on your 404 error page to ensure that it does an excellent job of helping your misguided visitors get back on track. This page should be a nice design which fits into your overall site theme. It's goal is to (a) tell your visitor what happened (or what may have happened) and provide some alternative ways to find out what they want. My own 404 page includes a site search engine, a link
to the site map, and the normal navigation menu.

Error pages: Others - There are about half a dozen error conditions (401, 402, 403, 404 and 500 come to mind) which can also happen occasionally. It is very wise to create individual error pages for each and every one of these. The other error codes can be especially confusing to some isitors so it's best to go out of your way to help them out.

As a side note, Microsoft IIS web server allows you to define a lot more pages for far more specific error conditions than Apache. If you are running IIS, it's a great idea to define customized versions for all of these codes.

Search failures - If you have an on-site search engine, be sure and spend some time on your search failure page. You want to help your visitors when they search but find no matches.

Common Misspellings - Another thing to remember is to include common misspellings in your pages for your search engine to find. You ca include these in the normal keyword meta-tags or, often, in search-engine-specific meta-tags (FreeFind and Atomz both allow for these special tags). This will help direct people to exactly the correct pages.

Helpful Forms - This is a little tougher, but when someone includes incorrect data on the form it's quite common to simply say "bad data" and force them to re-enter everything or guess what is incorrect. It's much smarter to clearly show exactly what is incorrect, and to allow the visitor to enter only the incorrect data again instead of the whole form.

Don't break the BACK button - Or any other browser control, for that matter. Your visitors should be able to back up, move forward or refresh their display at any time without any issues.

Keep Everything On One Page - If an error occurs, be sure the error message is displayed and the form or whatever is included (filled in with the user's previous values) on the same page. You want to prevent your visitors from having to back up or scroll to get to the form.

Highlight errors - When errors occur (especially in forms) be sure to make the mistakes stand out when you redisplay so they can be easily picked out from the rest of the page. It's also a good idea to include helpful hints on how to correct the problem.

Conclusions - The more you can help your visitors get to useful information and such, the more likely they are to come back and to recommend your site to others. So be sure to include contingency planning in your, well, planning.