There are dozens and dozens of different areas of SEO that can be explored: front end, back end, local or global are just the start. The aim of any SEO work is to generate more traffic to your site, without paying for it. This is referred to as 'natural' or 'organic' traffic. There are hundreds of limiting and varied contributing factors that effect SEO and where you rank within Google and honestly, nobody outside of Google really knows the magic behind it. All we know is that 'if I make this change, then this is the result' if that is the result you're after then keep optimising in the same way you were. If the change had a diverse effect then maybe you need to rethink what it is you're doing.
The way Google and other serach engines work is a mystery, and to make it harder it is a constantly changing thing. You think that adding some keywords to your site is telling Google 'this is what my site is all about, if people search for that then bring them here' and then all of a sudden, Google decides that (meta) keywords make no difference whatsoever. Funny isn't it. The goal posts keep moving but there are fundamental areas that remain the same and best practice will always yield improvements.
This is one of the more complicated aspects of marketing and if you're struggling in this area and need some help then get in touch today and let us make it Simple for you.