To discuss about SEO strategies the first thing that comes in our mind is the offensive strategies. This is the most common type of strategies that are being use by several SEO companies to raise their targeted website from their present position. This is however the most costly thing to be done for all the parties concerned. But there always remains the risk of being flagged as negative SEO, in this case.
On the contrary of the offensive strategies there are always the defensive strategies. These are designed to defend a position that the website already hold. This also creates barriers to the entry of new entrants in the market and ensuring that you may gain such position that no other can attack you and snatch your position. Therefore as it is very often that you may be a victim, its better to pick such a position so that you may not be attacked so easily. As for example if you get a Page Rank 7 or above there are more chances that others would not dare to challenge you.
One of the most interesting strategies are the flaking strategies. In this case you can befoul your competitors or your enemies that there is no real threat for them and in the last moment when they realize it is too late for them to take necessary actions. This can be something like launching social network in your niche but not focusing on the really critical areas while gaining some hidden advantage.
Besides these there are also the guerrilla SEO strategies that involve launching of lots of new small sites targeting specific keywords. However this tactics needs a really skilled SEO and highly disciplined one so that the others may not have the sense of what you are doing. And the thing that should be kept in mind is that the sites that you launch should not be same as the other.
Along with these there are also the deterrence SEO strategies. However this type of strategies are primarily negative and also not that much essential. But by doing this you can scare your competitors you can scare your competitors to leave you alone.