It is just like promoting any site, but requires more work due to the fact that there are more pages and likely a wider array of keywords to optimize and link for.
You will need to be a lot more specfic. Without knowing much about your website we can only point you towards guide. Here is a brief beginner guide I wrote for DP a little while ago: http://forums.digitalpoint.com/showthread.php?t=1635158
Sorry for the broad question. Since ecommerce sites use dymanic url, are there any issues to this in seo? Or does Google already loving dynamic urls that I don;t need to rewrite everything? Since ecommerce does not have to many content to promote what else can i do? Right now Im promoting an ecommerce site...I know some basic seo my concern is do I have to tell my client to use mod_rewrite or what this is to be more effective.
as already suggested, normal techniques apply, use of header tags, good copy writing, images with your keywords, look for modules which help change from dynamic url to seo url, back this up with a blog...
dickieknee has all the good points - standard SEO practices apply. but you may want a different approach when it comes to building backlinks. instead of getting every link you can get to the homepage, try getting some links to the individual product pages. for instance, if your site sells electronics, get some links to the cell phone section and some to the tv section, etc. those will ultimately lead to better sales (think Amazon and other big online stores).
i am handling a lot of e commerce and i am having a lot of success with those sites send me a pm if you have any question about e commerce
lots of quality work is required to maintain an e-commerce website............................do some keyword research............and other off page and on page optimization for your e-commerce website..........
Wow, well if i where you I would focus on creating a comprehensive site map and submitting it to google webmaster tools, large sites, especially Php dont index well without one. Also make sure to use URL's that reflect your targeted words rather than an item number.