Give people a reason to want to register. Create great content. Give them incentives. Tell them what's so great about joining and why they should do it. Promote your site through Facebook and twitter. Create a FB fan page. Encourage your FB friends to like and share your site.
Now a days SMO is in boom so first concentrate on it and secondly as your site is about for registration for any kind of services or so, you have to offer something interesting so that users may visit your site and for this you should run some adds as well.
Yes i accept Dani's reply, when a website has free offers , automatically visitors views the site and moreover sharing the content related to your site among social networking sites will create great popularity and increases traffic, blog commenting is a good way.
For my main website SNIP i use it for my programs and other stuff i make, so using my other website SNIP i am tracking how many times my programs are being downloaded and most of them seem to be a hit but i thought if people like my programs so much that they might register. NOTE: Most of my programs arnt useless some can be helpful.
I thought the only way i might get people to register is to make members only able to download my programs, but i don't want to be mean plus i don't want to force people to register. But i know what you all mean give the people a reason to register.
I was thinking about maybe making a suggestion system for my website so random people would say what they would like.
Also i just remembered only people with a hotmail email address can only register, thats only because it was too difficult to make a bit register system to suit different email address. If you have an easy way to send emails to different email servers using PHP.
Please tell me.
Also i have made a Facebook page SNIP and a YouTube SNIP
i have uploaded videos to "YouTube" on how to use some of my programs, the only comment i have gotton is for my program called SNIP
You'll have pros and cons if you decide to go ahead and deny the unregistered to your content as it may actually hurt traffic initially, but encourage repeat users to continue visiting.
In the end the website and what it offers is what will determine if users continute to visit or not - If you just continue to offer content as well as try to improve your SEO (by including blogs or other articles that are regularly updated, which is very good for SEO) you will just get a larger bulk of users, and statistically some of those users will give you feedback and your exposure will grow.