Let’s say you have the following keyword: “Winter tires”;
How should you get links to this keyword?
One solution would be to get all the links to “Winter tires”; in my opinion, this is rather inefficient, this may raise question for the search engines as the links don’t seem too natural;
On the other hand, varying the text to “winter tires 2011”, “winter tires – where to get them?”, “how to get winter tires?” is a good option; misspellings naturally occur too – “winnter tyres”; also, some people put nofollow links, others put image links, others put anchor text for “click here”;
Also, for a better-looking profile of links, it’s best to vary the place where you put a link (most natural place is in the content area, but how about the sidebar?);
How much should you vary? I would use this answer:
“This number varies widely based on keyword and industry. In template industries like people who sell wordpress templates or joomla templates, you can safely get 80 and 90% exact match anchor text. In other spaces, you need to keep it less than 10 or 15%.
The easiest thing to do is look at the top 10 in your space. Determine the average percent of exact match anchor text, then make it your goal to match that percentage. More importantly, get your Overall link metrics above your competitors, so while your percentages are in line, you have more in both quantity and quality than your competitors, but all within safe proportions.” (from here)
So, go vary!