What is the best and the most profitable and effective way to promote a website? Could you share some tips with me?

What kind of website are we talking about? Techniques used will largely depend on that.

Well, it is a video site which is not very big.

you may want to try Youtube or other similar sites
or post in thier forums

Without knowing the specific purpose of this site, or its target audience, I would say:

* put the site's URL in your signature in every forum possible. (Some forums may ask you to limit the number of links in your .sig, and you may have already hit that particular forum's upper limit. They may also have restrictions on types of links in member signatures. Check the various forum rules, or ask the mods.)

* go and comment on a few blogs who are read by your intended target audience. Make real, substantive comments, not the equivalent of "neat site". When the comment form asks for your URL, use the URL to this video site. (This works even better if you've been a regular commenter for some time, and so have built up a reputation as a repeat poster rather than a drive-by commenter.)

* make sure your site has a way for visitors to sign up for RSS feeds, newsletters, what have you (if your site has those things.)

These two may not be as effective, if it won't get your site's name and URL in front of your desired audience; but the suggestions are here nonetheless:

* quarter/semester break is coming up for many US colleges (community, junior college, vocational schools, colleges, universities). If your intended audience / user base includes college students, see about making up and distributing flyers at nearby colleges. (If they have cork boards or kiosks, the colleges may require that people get permission to post flyers. Once you get permission, your flyer will not only be put up and left in place, it might not be covered by a whole bunch of other flyers put up by other folks - because they have to have permission, as well.)

* Halloween's coming, in some places. If your target audience is young adults, see about putting flyers at local events, haunted houses, clubs having Halloween-themed events, and so forth. Pick places near you so that you don't wear yourself out distributing the flyers - and to minimize your losses if this particular option doesn't get you many visitors/users.

It's true... Forum posting with signature of ur URL and also articles writing and blogs.. submit them to website articles with your company name n URL...

Also, do copywriting or marketing writing for your company.. Plus, do social bookmarking and directory listing for your website

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Also don't forget about doing SEO on regular basis for your website to gain better rankings in the search.

Try for SEO, youtube and forum..

forum postings

Anything you can do will be good, of course. One that I didn't see mentioned here is to use social bookmarking and networking sites often. Add buttons below your videos to encourage your viewers to bookmark them, too.

What foruns?