For most modern search engines (Google included), the main thing you need to do in order to get any decent ranking is try to build in-bound links (also called "backlinks") to your website from other sites. The simplest ways to do this are:

1) Add links to your new site from any other websites you own or run. The more closely related the content of the other sites to your new site, the better.

2) Submit your site to free directories. There are thousands of these around, so this can be time consuming, and the return isn't huge either, but it's a way to get started.

3) Contact any other sites that have similar or related content to yours, and ask them nicely if they'd consider linking to your site. It might be worth offering to link back to them. Of course, how likely people are to link to you varies from sector to sector - you're more likely to get links back from people who aren't in direct commercial competition to you!

As has been said, WebPlus does all the "on-site" SEO for you - at the design stage stay focused on producing decent content and you'll be fine. The part of SEO you'll need to invest time in after your site has launched is link building.

For more info on how link building helps your ranking try here: http://en.wikipedia.org/wiki/PageRank

Cheers,

Dave

Serif forum link - Search engines

And, Dave also wrote:
Honestly, if you haven't changed the content that much and your site isn't brand new, what's most likely to affect your search engine ranks are external things like incoming links (and the rank of the sites the incoming links are on) and changes in the SE's ranking algorithms. e.g. Google updates its index periodically; sometimes they'll have tweaked the algo, sometimes not; it's virtually guaranteed that the "graph" of the web has shifted around quite significantly between updates.