Do Follow or No Follow?

[onefor1two]

When I want to link exchange with some other website or when commenting, do I need dofollow links or nofollow link.

on what links should I concentrate on?

if concentrate any one links, is that does effects my site popularity, PR...etc?

[convergent]

When I want to link exchange with some other website or when commenting, do I need dofollow links or nofollow link.

Link exchange is up to your agreement. In your own forum better do nofollow links to escape from spam writers

on what links should I concentrate on?

for inbound links you are better to use both the same time. Only dofollow links are suspicious

if concentrate any one links, is that does effects my site popularity, PR...etc?

never concentrate any one link

[onefor1two]

Thank you, Convergent

[seo123]

Do follow is obviously good and will help you in ranking but that doesn't mean no follow will penalize you, some good sites also provide you no follow tag but since it's a quality link so its important. 

[wjmntg]

I think, need dofollow links

[tinjuashok]

When I want to link exchange with some other website

If you want to link exchange adding a rel="nofollow" attribute to the <a> tag.

[Ken]

You should concentrate on building do-follow links because they are the source of increasing website's page rank and improving visibility of keywords in search engine results.

[nickie snyder]

Do follow links provide you with better "link juice" which helps in boosting your rankings on search engine. No follow links also generate referral traffic, so mixture of both must be followed to create a "natural" link profile.

[casinobook03]

Do follow links provide you better result in ranking.They are indexing in Google crawler fast.Some good sites have no follow links,but they give good result.

[coolguy27]

When I want to link exchange with some other website or when commenting, do I need dofollow links or nofollow link.

on what links should I concentrate on?

if concentrate any one links, is that does effects my site popularity, PR...etc?

Minimize your linkexchange according to Jim Boykin. Here some post artcle about it: http://www.awebguy.com/2011/02/reciprocal-link-exchanges-dont-work/

Matt Cutts (and common sense) said this: "the best links are earned and given by choice." Unless common sense is a totally worthless concept, what Matt said still holds true today, tomorrow, and always.- http://www.mattcutts.com/blog/seo-mistakes-link-exchange-emails/

Try to get as many different link types as possible. Here's a good lists:

    Editorial citations – getting mentioned within the context of an article from a blog or news website.
    Resource links – getting mentioned in a list of links pertaining to the topic or subject matter.
    Web directories – There are a ton of them, but for the most part, they can be split up into:
        General – directories listing websites from every corner of the Web.
        Niche – directories listing websites only on your topic matter; i.e. an environmental directory only listing environmentally friendly websites.
        Local – directories listing websites only in a certain geographical area.
    Blog comments – Leaving a comment with your name as the anchor text of what will most likely be a nofollow link.
    Forum discussions – Getting mentioned in a forum in the context of a discussion.
    Profile pages – Listing your website on your profile page if the website allows one.
    Web 2.0 + article directories – Getting a link in the context of an article or Web 2.0 property.
    Author Bios – getting a link in the bio you provide for a guest post or contribution.
    Image links – linking an image, possibly with a keyword rich ALT tag, instead of text.

About nofollow and dofollow: Mixed it up because Google wants natural links. If you only do dofollow links Google will think it is manipulated links but if you mix those two (dofollow and nofollow) Google will think you are building naturally.