First let's start with definitions:
SEO:Search Engine Optimization, SFO: Search Friendly Optimization.
These two things are what most webmasters have trouble balancing. These things seem to always be on opposite ends. On one hand you have to make sure search engines can crawll your website without any problems. On the other you have to keep the site looking good to keep your visitors.
These are all based on what kind of site you plan on making. A corporate website selling shoes in the real world might focus on keeping the site looking good to visitors. And maybe pack it up with flash and all kinds of descriptive images. On the other side a site about online products, e-commerce, might cut back on the images and focus on seo. I will go into both of these just in case.
Let's start with seo. The first thing you need if you choose seo is to meta tags. Now there many meta tags generators out there for a quicker way to make them. But I suggest like me you make them yourself according to the search engines you want your site to better perform at. In short you have to study those search engines and find out how they get their content and what meta tags they require or may find usefull. Mine is based on goole so check out the source of the blog and those are the tags that google uses. Also a site that may help you out with your seo is:
http://sitesubmit.ca/ they require you to be a member to ue their tools but it's worth plus it's free. They have many seo tips and tools. In your reaserch of the search engine don't forget ranking. Find out what they base their search results on and how they decide which results show up first when a user queries. Like google uses google googlerank and overall page rank. But you may hav eto increase your content on a subject in order to increase your keyword density and such.
Second sfo. SFO is fairly easy to accomplish once you have the right info. Like many sites they host regular polls and surveys about what users like and their personnal opinions. It's an effective way of knowing your audience. Once you know most of your visitors like certain kinds of things you start providing them.
Therefore pleasing your users and making a successful site. But never forget about the stalistics the users don't need to tell you. Like what browsers usually visit your site and what operatinf systems they use. And as many webmasters know firefox and internet exploer(leading browsers) have different rendering engines.
So find out which most of your users use and customize your site to it. Also if the stalistics show that they have just about equal users use what we a splash page. To allow the user to show which version of the site they want to view. Two versions of your site may be hard to keep up but remember it's worth it. In one case one of my friends had to do four different versions. And keep them updated at the same time.
But also you may have to balance the two together if you want them both. Though it is hard it may be for the best.