analyse where you lost traffic, incase of search engine, then you need to think about your content and backlink to your pages or site. The best is rewrite the pages which you think you are loosing your traffic.
Simple tip is: Check out your Google analytic visitors sources. Try increase the promotion in most visited sites (sources) with most visited keywords.
Do some SMO activities, help you to improve traffic.(Facebook, Twitter, Linked In and My Space are Social Networking Sites)
Digital marketing is the one of the best solutions. Yep, it requires some money but if you want a big traffic or stop losing your website traffic it is beneficial. Also put the good quality content on your website which is also must to stay the traffic at your website and people may came to back there.
Best way to get traffic is be attached with social media activities and publish press release and do blog commenting..Make sure you use keywords while linking you website.
First focus on,which part of your website is responsible for that.Worked on these pages. you can devote more time on Social media site so that you will get the good traffic on your site by posting latest updates.