I am not SEO field person and pure java/j2ee based person so while reading i came to know that we need to submit website to some well known Directories over internet, not sure how much truth in this.
My question is if its true from where i can get a relevant list of such Directories or any resource which can help me in this regard. Additionally what other things needs to be taken care with respect to SEO in the initial phase of the portal.
Submitting to directories can have a positive effect on your rankings but, generally speaking, in reality unless you are targeting a very niche market/search term I wouldn't expect to see great or significant results from this. The overwhelming vast majority of directories rank poorly and have few incoming links to them. So their SEO value is minimal (virtually zero). So listings in them will give you very weak links pointing to your website. Weak links do add up but very slowly. So if you're targeting a broad market or search term you will never reach "critical mass" this way. But for very niche markets and search terms it may not take much to rank well and thus these links can be helpful.
If you're looking for directories to submit your site look for directories of directories like directorycritic.com.
