you've done 6 months of SEO for a site and there haven't been any improvements, how would I diagnose the problem?
Providing a little more information about what kind of strategies and techniques you have resorted too and have you optimized your site on-page will be of a good help to provide or sort out a solution.
Use online tools to find out how many backlinks you have majesticseo . com is a very good site for that and if you have installed Google analytics you can check the traffic growth day by day and the pages that get most visits of your site and optimize them based on that analyze details. Like others asked it's easy to guide you if you tell us little bit more about what you've done to optimize that site.
Continuous changing of your sites SEO settings and links would be the repercussion of this. If something is set in stone, leave it be. Just because nothing happens for a few days or so doesn't mean it's not working, you just have to be patient but if you change it often... you will see "NOTHING" because the spiders are gonna keep crawling changed content and never have a correct location or link.
If you were to: 1.) Research your niche and find longtailed keywords with higher traffic and little competition and incorporated those keywords in to your web site and url scheme 2.) Focus on building quality links with in your niche 3.) Apply social media techniques to make your site more interactive 4.) Redesign your web site so it is more aesthetically pleasing and user friendly 5.) Focus on more keyword rich content (see #1).. start a blog.. or an article section on your site 6.) Clean up your HTML and coding you WOULD see a drastic difference in traffic even if it was just 25 people a day... If you aren't seeing an increase in traffic then you either don't know what you are doing or you are just doing it wrong.
If we know what you were doing as far as SEO, it would help. Be specific -- What PR backlinks were you using? Can you give us the website to analyze? How often were you posting content? etc...
EVERYTHING that involves SEO takes time...but looking at the quality of articles the types of sites you are linking to...will give you insight on what is not working. Take a look at keyword density. Search for short and long keyword phrases that are low to mid level competitive phrases.
In fact, changes you make today will take affect in 1 month-3 months. Point proven: On one of my web sites I was linking to a blacklisted web site AND I have a series of links leading to invalid pages. I corrected those changes and was disappointed that nothing changed. 2 months later all of a sudden the site tripled in traffic.