First of all don't be fooled by SEO professionals. 95% of the offers are scam. The rest are serious professionals, but unless you are running a million dollar business you don't need them. Just follow these 5 suggestions and you can be sure you've done everything you can to rank high in Google.

1. Include the keywords in your domain name, page title and h1 article title. So for example if you want to sell squirrel food, register the domain squirrelfoodforsale.com. Include the keywords Squirrel Food in the page title and h1 article title. Include the same keywords in the body copy as well, but don't overdo it. Just make it natural.
2. Make sure as many related sites link you as possible. Not only the link has to include your keywords but the title of the article linking you should include it too. So if petfood.com links your site from the article Feeding your squirrel then you've got a valuable link.
3. Use Analytics and AdSense on your page, so Google can monitor the traffic of your site and make sure many people visit your page.
4. Update your site and page often. Google gives priority to content that has been updated within a week for obvious reasons.
5. Avoid links from spam and fake sites. You can get blacklisted easily and you will do more harm with such links than good.

Don't spend too much time on SEO, working on your product is time better spent, because there is nothing better than being linked organically.