It’s a tough question to answer – partly because I’m not Google and don’t have any insight into your particular situation and partly because each time it happens it is different. I’m also not an SEO expert am won’t give you any technical advice – but let me give you some general advice to start with:

1. Don’t Panic

I’ve had this happen to me at least 5 times over the last 7 years of blogging and most successful bloggers I know can recall a similar number of Google fluctuations that have brought decreases (and increases) in traffic in their blogging history. It happens to us all – sometimes in big ways and sometimes in small ways. In chatting with one Google employee recently he told me that they are making daily (and more) changes to the way that they rank sites (mainly small tweaks) so over time we’ll all notice changes.

The key is not to make massive big changes to your site’s SEO too quickly or as a gut reaction to a change in your ranking.

For me the first time that this happened (when I lost 70% of my traffic) I was very tempted to make big changes to my site to try to fix things. I was advised by a few wise and experienced web masters to wait. I did and a few weeks later almost all of the traffic returned. Google fixed itself (phew).

If the traffic doesn’t come back after an extended period you might want to get some expert SEO advice and make some larger changes – but I personally am glad that I’d seen out the dips in traffic rather than doing anything to hurt my long term rankings.

Of course there are times when you might need to make some changes…. such as….

2. Have You Done Anything Black Hat?

Google has guidelines in place for webmasters. If you want to rank well in their search engine you need to play by their rules. Of course there’s a whole industry around ‘bending’ and ‘manipulating’ the rules and many web masters make a living by doing it – however if you are caught breaking the rules by Google you’re likely to be penalized.

If this is the case for you you have two choice:

I know of numerous bloggers who’ve asked for reconsideration and have been reinstated back into the index. It can take a little while (the last one said it took a couple of weeks for them) but in the long run it can be well worthwhile.

3. Build Other Sources of Traffic

The biggest lesson that I learned back in 2004 when I lost most of my traffic as a result of a Google algorithm change was that I needed to diversify my approach to building traffic to my blogs.

Up until that time I was almost exclusively working on driving traffic via Google. It was like a drug that I’d become dependent upon in some ways and much of my day was spent writing content for Google and attempting to ‘get links’ to that content from other sites. I was not really writing for regular readers or trying to build community on my blog – I just wanted traffic that I hoped would click my ads and affiliate programs.

This approach had worked for me – however when my Google traffic disappeared I was left with little and realized how short sighted I’d been. I began to change my focus and started working on other sources of traffic.

I still love the traffic that Google sends me but today if it all disappeared it would hurt – but it wouldn’t be the end for my business. Next week I want to followup this post with another one looking at some of the ways to become less reliant upon Google traffic and to build traffic from other sources – stay tuned for more.