A useful metric must be:
Relevant – Does it align with core business goals? If you move the number, will it result in positive change?
Measurable – Is the value subjective? Can you define it? Is it possible to technically capture the data?
Actionable – Can you do something positive and impactful with the data?
Reliable – Is the metric technically robust? Will it be relevant in a year? Can it track progress over time?
Readable – Can it be easily misunderstood? Does it require a lot of context? Could it lead to bizarre behaviors? Does it suffer a lag that makes it difficult to evaluate?
Here is a big list of metrics you can consider measuring. But choose only a few that could really make a difference for your product.
Classic
Conversion (sales / visits)
Product page conversion (sales / visits to product page)
Funnel analysis
Basket abandonment
Bounce rate
Sales
Leads
Subscribers
Unique visitors
Returning visitors
Page views per visit
Visit to order ratio
Load time
Registrations
Visit / session length
Page views per visit
Time on page
Time on site
Form abandonment
Failed internal search
Referring pages / links
Geographic locations
Print page
Banners
Click through rate
Impressions
Financial / sales / business
Average order value
Basket value
Profit margin
Average sales price
Cross sell
Gross margin
Category margin
Cost per lead
Customer acquisition cost
Lifetime customer value
Average customer value
Membership / subscription churn
RSS
Feedburner subscriptions
Shares on Google Reader
Call / customer contact centre
Average call length
Support vs sales calls
Inbound vs outbound calls
Web generated calls (unique number on website)
Web fulfilled information calls
SEO
SEM keyword value
SEO positioning
Changes in SERP results/rankings
Top entry pages
Number of keywords triggering results for your site
Number of clicks to your site from keywords
Google trends
Inbound links (back link discovery)
Percentage share of each engine
Branded vs non*branded searches
Affiliate links
Affiliate fees
Social media
Facebook referrals
Incoming Twitter links
Facebook sends/shares/mentions
Facebook likes
Facebook fans
Facebook fan rates
Tweets
Retweets
@s on Twitter
Twitter followers
Twitter follow rate
Google +1s
Bookmarks on Delicious
StumbleUpon thumbs up
StumpleUpon reviews
Diggs
Google BlogSearch links
Blog comments
Blog articles
Video views
Youtube favourites
Youtube channel subscriptions
Youtube channel comments
Youtube video reviews
Slideshare views
Forum mentions
Thread size
Online review mentions
Stars in reviews
Bit.ly / URL shorteners usage / clicks
Third party / benchmarks
Comscore
Hitwise
Alexa
Compete (US)
Email & campaigns
Email newsletter churn
Email sign-up
Emails sent
Emails bounced (bad address)
Email forwards
Email campaigns
Open rate
Delivery rate (sent – bounces)
Click through rate (CTR)
Email related to conversion / other metric
Unsubscribe rate
SMS subscribers
Via print publication / 3rd party (unique URLs)
Internal search
Search no results
# Search 1 to 10 results
# Search 10 to 25 results
# Search over 50 results
IA:
GOMS technique
Time to content
Clicks to content
Back button clicks
Task completion
Errors
User testing metrics:
Words Recognition Rate
Reported expectations and performance
Facial reaction
Number of back presses
Gap satisfaction
Path’s taken as a measure of scent
Work-flow matches mental model or not
Satisfaction measurements:
Net Promoter Score
ASQ PDF: After Scenario Questionnaire (3 Questions)
NASA-TLX : NASA’s task load index is a measure of mental effort (5 Questions)
SMEQPDF: Subjective Mental Effort Questionnaire
UMEPDF : Usability Magnitude Estimation
SEQ PDF: Single Ease Question
SUS: System Usability Scale or sometimes the Single usability score (why it needs two names I don’t know)