Principles for good web-based experiments
WEB EXPERIMENTS MUST BE GOOD WEB SITES
To do a good web-based experiment, a researcher needs to keep the drop-out rate as low as possible. Good Web design is key to getting people to take experiments seriously and to finish what they start. By encouraging good coding practices, it also improves cross-platform and cross-browser performance.
DSN likes the simple heuristics-based approach of the book Defensive Design for the Web by 37signals, Matthew Linderman, and Jason Fried, which contains 40 practical guidelines for how to improve a site.