SEO services, you'll be surprised to see how many offers there are, some of them even promising to help you for free. Choosing your SEO provider is extremely important, because this choice can make you huge or break you for good. Harmful actions are very hard if not impossible to undo, therefore you should treat SEO with great care and make sure your agency follows the best practices in both on-page and off-page optimization.
Here's an infographic to help you make yourself an idea about on-page SEO best practice. We are going to see what are the most important elements on a page that will communicate to search engines that your content is relevant for such and such keywords or niches. Refer to this article when you evaluate your SEO service providers and see if they are working by the book or trying to find their way to the top using shady methods.
Although not a direct influence factor for your position in SERPs, the meta description is very important because it is the text that shows on the results page for your website. It needs to be compelling, to entice people to click on that particular result in order to end up on your actual website. In case you don't write a meta description, search engines will take a bit of text from your page and will display it, but you won't be able to control it. This is why you should sit down, take your time and write your best piece of advertising to make viewers click. The meta description should be restricted to 156 characters or less.
The title tag is perhaps the most important on-page SEO element. It should start with your main keyword and it should contain maximum 70 characters, because that's the limit in Google search result pages. This element is important for both humans and search engine robots, so you should spend some time and write the best and most concise titles you can.
Other important elements any good SEO service should pay attention to are the heading tags, the URL structure, the keyword repetition and prominence, the keyword variance, the image optimization, the spelling, grammar and readability of your writing, the avoidance of duplicate content, the social signals, the presence of the Google Authorship markup on your page, the internal linking structure, the presence of a sitemap, the page loading times and the outbound link quality.
It's a good idea to always link out to your references and sources, but you should also try to limit outbound links on a page to maximum 150. The more authority your sources have, the better it is for you. Avoid linking out to sites that aren't trustworthy, because things you link to act as a relevancy factor in Google's ranking algorithms. You only want to send quality signals, so you should be very careful whom you associate yourself with.
For more in-depth details, study this infographic and check your site against it and consider these information in making sure that you have the best service may it be expensive or affordable SEO service, to see how good your on-page SEO is.