Simply put. YES
There is too much in this question to answer in one blog so I will tackle what I think is the biggest mistake. Bad code. It is that simple. If you have a bunch of broken links, and your navigation is not working, images without alt tags, then your website will never pass a validation. One thing to help ensure the integrity of your design is to use CSS (Custom Style Sheet) or a CMS (Content Management System). This will ensure that all your code is clean, all your links are working, and no un wanted code is included. You would not believe how this can effect your rankings. The crawlers will have an easier time going through a site that is perfect and will reward it much easier than a site with bad code. It's that simple.