There are people out there who are doing SEO for clients, who write unique content and get links for a client. I 100% agree that both of these are important from a ranking point of view but are they that important if your website technically isn't set up well?
My opinion on that is NO, you can lay link after link from some of the best sites in the world but if your technical SEO isn't sound then it's not really going to have the desired impact. People often think that SEO sounds too easy to be true, a few links and a few articles and all these rankings appear. On a daily basis I get people contacting me asking for an opinion or a website audit and the results are alarming. Very basic fixes on the technical side often go unnoticed because people don't do site audits or simply don't understand how Google crawls a website or how websites need to be structured to do well on the search engines.
I was having a good conversation with Dawn Anderson & Peter Nikolow about some of the horror stories we come across and how some very basic technical fixes are often left unnoticed and it's these technical fixes that can make all the difference. 
So what is Technical SEO
Technical SEO isn't a few minor tweaks, it can get very complex but doing regular site audits, server log analysis and using other analytics tools will help you understand how your website is functioning and how the search engines, in particular, are seeing your website. Some of the most common problems we see with websites from a technical point of view that some other SEO's often miss include:
- Making the bot experience as good as user experience
- Slow Loading Speed
- Mixed Content due to a poor SSL migration
- Temporary redirects used rather than 301 redirects
- Lack of understanding on how CSS, JS and other code works
There is so much more too that I will cover off in a little more detail below as the above are just some of the basic's but there is so much that goes on in the back end of a website that you want to ensure you can use any of these fixes to get leverage on your competition.
Website Architecture
Websites are always growing and some thought needs to go into the site structure, especially where E-commerce websites are concerned and some of these Technical SEO fixes need to be done. There will have to be regular checks and audits done on your site to ensure that you are also on top of your game. Over and above all of the basic on-page SEO such as title tags, unique content, image tagging, meta descriptions and implementing your keywords after hours of research and competitor analysis there is a lot more to think about before you go away and start your link building efforts.
- Using your robots.txt file to instruct search engines appropriately and maybe no index specific URLs
- Canonicalisation
- Cannibalisation
- Formatting of URLs
- Using the correct parameters for dynamic content such as product filters etc
- Pagination
- Structured Data
- Internal linking
- & much more
Log File Analysis
After you do all of the above you then move onto log file analysis, now this is an area that is often missed out. In my experience some SEO's don't even do regular site audits let alone look at the server logs and understand how the search engines are crawling your website. Correcting any problems on your website will lead to better rankings, more sales and more money in the till for a business, so I'm not sure why people ignore this area on a frequent basis. There are tools to help you with this analysis such as Splunk, GoAccess, Logzio and many others that will be able to help you identify any issues.
The most important part of Log Analysis for me is that you want to make sure that Google is crawling and indexing all of the pages you want to rank on a website ( and nothing else ) forget about filter pages, contact pages and many other no value pages ranking well.
You want to analyse any error codes as too many of these will cause the search engines to reduce crawling your website which can lead to a drop in pages being indexed and rankings dropping.
In terms of keeping on top of your response codes, you want to ensure that you have no broken links, 404 errors or 302 redirects. 302 redirects do not pass any link juice and in almost every case should be a 301 redirect. ( Kick your developer for doing this ).
Crawl Budget
This is something you also need to keep a close eye on, you don't want the search engines crawling all of your duplicate URLs, or any URLs that your SEO suggests are not important.
For example, your analysis may guide you to the fact that Google will give you a crawl budget of 1000 pages per day, you want the search engines crawling your pages that are designed to rank ( nothing else ) You don't want your scripts, duplicate URLs or any other pointless page eating into your crawl budget. This is the type of data your Log Analysis will give you. How important is it for the search engines to find your pages designed to rank? It's essential in my opinion and this is the depths you have to go to if you want to perform SEO at the highest possible level.
So, this gives you an insight into some of the things that a Technical SEO would do for your website. A good all round SEO will have been using these things to rank well for many years, but Technical SEO is a word that is loosely thrown around these days by SEO's who are doing nothing more than some very basic on-page SEO.
Website Speed
As you will see from the image above, my own website does need to pick up a little in terms of speed and this is an area that I'm working on. It has improved a great deal over recent weeks, but I will continue to work on this as I want it to be as fast as humanly possible without stripping out any of the functions and features.
Website speed is vital and I believe it is a very important ranking signal. It is very easy to check how quick your website is by using tools like Googles Page Speed Insights, GXMetrix or Pingdom. It's vital to understand and resolve anything that is slowing your website down, whether that is a poor server, images that are too big, or minifying CSS and Javascript on your website. There are additional caching plugins or content delivery networks such as Cloudflare you can bring into play to help with some of this too.
Technical SEO is always going to be an important part of the SEO process, equally as important as any other part of SEO but they do all combine to provide you with a strong website with high rankings and traffic if done properly.