Build high quality Links
Gone are the days when Google used to rely on the quantity of links for ranking a website, it now considers the quality of your backlinks for ranking and penalizing. Poor quality links built with little efforts are Google's easy target for penalty, so do little more than just directory submissions and stop spamming with blog comments.
Expand your network
High quality links are not easy to build. You need to have a strong and wide network of SEO experts to assist you in link building campaigns. Each and every SEO or webmaster has huge network, he can introduce you to new connections and help you get high quality links.
Don't stick to one method
If you stop trying new things, you increase the risk to get bored of your life. People love variety in everything and so is Google. Check your link profile, if you have stuck to a single method, move forward before your ranking drops. Create a combination of old and new methods and use it intelligently.
Monitor your website
Although SEO monitoring is very important, it is overlooked by many SEOs. If your content is not indexed, all optimization efforts will go in vain. Monitor your traffic, uptime and pages you noindex with meta tags or robots.txt.
Don't change the URL
Some webmasters change URLs when they redesign without thinking that their rankings can bounce. Change is risky, especially if it is related to URL. No matter how perfectly you have executed the URL change, errors can occur and some pages can lose ranking permanently. Avoid changing the URLs.
The mighty Google is intelligent; you have to be more intelligent when playing with it. Good Luck!