We like to think of a linking campaign as a constant, never ending crusade to get other sites to place a well formatted link to one of your sites. To discover how many people are currently linking to your site, you can go to either www.google.com or www.alltheweb.com and use a link search. Click on either of the previous two links to see what both Google and AllTheWeb return for the web site www.altavista.com. You can now change the domain name yahoo.com to what ever one of you sites you want to check. Please feel free to use the form below as well.
Enter your domain in the following forms following the key "link:".
Now that you have a way to check the number of inbound links to your site, you can start tracking that number over time and use it as a metric on your site's health and strength. You should also set goals for the amount of links that you will attempt to get every month. This is a time consuming activity; it's a whole bunch of work, but stick with it, and it will all work out in the end.
You can also use the link key word searches to help do research on your competitors. If some site is linking to your competitors, or someone in your space, then you should attempt to get a link from them as well.
Now most schools of thought say that any link is a good link, and that might be true. But one does not have all the time nor money in the world to get everyone to link to them. So pick and choose who you want to work with. Additionally, if you do get a link from a site, make sure that it is a site that you want to associate with. Just because they are handing out links, does not mean that they are worthy.
There is also something that Google tracks - a bad neighborhood listing. I have not seen a good clean definition of this, but basically you want to stay away from sites that practice shady tactics. One easy way to test this is if the site in question is carrying some sort of penalty with Google. I wish I could explain how to do this, but we are still trying to get a better definition ourselves. If you can determine that the site you want to link to is of good standing, and 99.9% of the sites are in good standing, then throw a link up on your site to theirs. No, just don't place stuff site nilly, but rather what makes sense for your customers. If you can honestly say that a link here or there makes sense, then do it. Don't go over board; don't turn your site into a little link farm.
Internal linking should be done whenever it makes sense. You should have a clean navigation and a way for users to get to your search and home page easily. If a section of your site deals with something covered in a different part of the site, by all means link to that section of the site. You can also use this technique to distribute power from some of your internal pages, to help boost the strength of another page. For example, you have a site about widgets (a made up thing that does not actually exist, or does it? www.widget.com) and you have many different styles of widgets. One style of widget is the Open Source widget, and you have ten different types of those. You could then create a new page just to talk all about open source, then point your ten, on topic, relevant pages to your new open source page. We do this on this site from time to time with the html section of the site. This is not to move page rank or anything, it's just for information and ease of use. But you can also use it for a boost.