Just read a nice little blog post about what to look out for when deciding over whether to acquire a link or not.  I thought I would expand this with my own thoughts and processes.

-Relevance

The importance of this CANNOT be overstated.  Google rewards relevance in terms of SEO and PPC listings and so it is vital that you in the first instance, try and obtain links from relevant sites.  Moreover the link will be of greater SEO value if it is linking to a relevant, similar themed site.  It will also, from my experience, pass more PageRank.  There are other factors to lookout for, but I would argue that this is THE most important factor to look for.

-No Follow

Obvious to many, but vital that the link does not have the no follow attribute attached to it.  You can find this out by click the right hand button on your mouse over the link and then choosing “properties” from the Firefox menu.  It will either say “external no follow” or “Same Window”.  External no follows means exactly what is says…a no follow link.

If you are using internet explorer to do this, the method doesn’t work so you would need to check the source code which is more complex and takes longer.  Switch to Firefox ASAP!

-PageRank

People get hung up on PageRank to the point of obsession.  It is important and getting links from sites / pages with a high PageRank will aid your rankings and trust rating.  However it should not be the only tenant you look for in a link.  Think about the relevance, then the PR, if you can get both it is a bonus

-Domain Age

Overlooked by many in my opinion, but the age of the site where the link is from is also very important. Google likes old things, which is why it is easier to SEO older sites compared with new one’s and why new sites can be Sandboxed. The same principle applies to links – links from older domains are worth more than links from newer ones (assuming all other attributes are equal of course!)

To find the domain’s age use either the Netcraft Toolbar or the new SEObook Toolbar. Below is a screenshot of both.

- Caching

Checking to see whether the page where the potential link will be has been cached should also be checked.  Whats the point in a link from a page Google hasn’t cached?  To do this use the Google Toolbar and the cached menu option (below)

-Number of links to Page

The amount and quality of the links that link to the page you want to link from will be what contribute towards it’s relative value and strength.  Using the SEObook toolbar again, you can see how many links are pointing towards any website’s domain.

Typical sites with lots of inlinks include .edu and .gov sites as well as news sources – links from these are highly sought after and great for SEO.

-What else on the page?

If the page is full of other links, as in overly full, your potential link is not likely to carry as much weight, especially if they link out to non relevant sites.  In fact the whole page will be devalued.  The best link would be mid paragraph, with a relevant anchor text.