It seems like Google is updating their programming and how they rank your website every week. Some changes impact you immediately and others will take longer. Don't wait until your visitors drop off. Regaining momentum is more costly than maintaining your internet authority.
If you are managing your marketing yourself if takes a lot of time to stay informed and then execute updates to keep your website visible. In some cases you won't know what the change will do and whether you can deflect the impact. Please understand that publishing a website does not mean you will get visitors and sales. It is the same as a store front. It has to be marketed, promoted in every way you can, not just inviting your family.
Knowing when to hire a professional to manage your SEO and internet marketing should be part of your business plan.
There are companies that offer low priced monthly subscription for SEO. If you have very little budget I recommend you at least pay for that - but compare company offerings so you know what you get and don't get from the service. These companies are selling bulk services so don't expect that the services will be personalized or provide results that a fortune 500 company is getting.
Simple metrics from Google analytics will help you see the results, but it is like anticipating the stock market. X + Y isn't guaranteed to = Z. When you are ready to be more aggressive and delegate the marketing so you can focus on your business, it's time to interview and hire a marketing company.
Learn about optimizing your landing pages in our free ebook.
For more information check out this article on recent Google changes.