Source: http://blog.hubspot.com/marketing/what-to-do-if-website-traffic-is-down
Google continuously makes algorithm changes so some changes in your traffic stats is inevitable. But if you start to see any unusual changes in your website performance numbers, it might be time to take a deeper look at the situation and try the following steps to recover from the dip.
1. Review your code.
Your tracking code may have been accidentally deleted, for instance. Use Google Analytics or a similar marketing automation tool to monitor your website performance and get accurate data about your website visits.
2. Check your keywords.
Make sure to refresh your keyword tactic on a regular basis. What works last week may become outdated next week. Set up keyword tracking to make sure you are targeting relevant search terms in your market.
3. Monitor your site’s authority level.
Keep an eye on your websites authority through tools such as the Moz’s Domain Authority. Based on your findings, you can then carry out additional tactics such as improving your content or doing outreach to more high quality sites to improve your rankings.
4. Hunt for bad backlinks.
You could be penalized for toxic backlinks without you knowing it. So make sure to audit your referral links to uncover those that might harm you, and start cleaning up your site.
5. Get expert help.
If after doing steps 1 to 4, and you still find many issues in your traffic stats, the best path to take is to order a website report from an outside specialist. This way, you can really identify the problems and then make smarter decisions for the good of your website.