Simply put. YES
There is to 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 (Contnet 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 belive 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 then a site with bad code. Its that simple.