First, make sure your tracking system is very user friendly.
It has to be easy to access. Does your client have to go to a web page to file a bug? Is the application buried deep in the sitemap? Nobody is going to open a browser, find your site and go through numerous links just to file a bug. This can be solved by putting a link in your application (again, it has to be easy to find; like Help > Report a bug). If your client has more then one application, make sure he is directed to correct page (or pre-fill the needed fields).
Next, do not require of your client to classify the bug (like severity and whether it is in fact a bug or a feature request). Also keep number of fields low. Description and a screenshot is plenty.
Make your controls easy to use. Nothing is more frustrating like having to wrestle a datetime picker with three drop-downs when you are trying to get some work done (and of course if you select day 31 and then April, day gets reset to blank value).
If you expect a screenshot, give your client a nice silverlight control, where he can just drop the file instead of searching it all over his disk.
When your bug filler is customized so your own mother can use it, you'll still have to push a bit. Try to "forget" about the email sometime and when the call comes act surprised and ensure your client that you received no bug report from him. Of course when he insists that he did send it to your email, have an "ah" moment and inform him your email is acting "strange" lately, then ask him to resend the email. Next bug report will be filled right.