User referrals can be a hugely powerful tool for growing your user base. By optimizing your referral process, you can increase your viral coefficient, and work towards a tipping-point of exponential growth:

• Explicitly ask for referrals
• Offer referral incentives to existing users and new signups
• Tell your users who to invite (colleagues, their boss etc.)
• Ask for a referral after a positive user experience
• Ask again!