A domain name becomes a Brand. In the scenario we are living, Marketing is very fast merging into online marketing. I think in less than 2 years marketing would only mean online marketing. You must take domain name for your website very seriously. It is paramount to your success. Businesses cannot be built solely on domain names but poor strategy on this front may create serious obstacles against your online venture. It should have some basic qualities like,
Dot coms are the best bet
It should be .com, preferably, unless you are part of a big network and want some geographical/professional... emphasis. if you don't get the desired one, find another. Non .com domains often lose their traffic to their .com competitors. Don't say all .com have got exhausted. Its a hogwash, perpetrated by some domain sellers. Be innovative, you would still find .com, in killer category. I recently have found two.
Easy to Remember
It should be easy to remember. Use something unique, or commonly known words. You should not use a complex word, which are difficult to recall. Good domains have good recall value.
Keywords are good but exceptions are there!
It may have word which are part of few search query with good volume, but not necessarily. If you are lucky, you would get one. However, don't make it your stumbling block. Many successful are not having this trait. Mashable & lifehacker, are just few of them. They have made their success through internet though.
Big Name typo gets no respect from visitors
Avoid being a typo of a big name. Most of the time you would find they are already taken. It may be good from adsense revenue point of view, but definitely not from branding point of view. Can you name someone successful around some big name? You simply lose the trust and respect of your visitor.
Hyphenated Domain Names
Avoid hyphenated domain names. Hyphenated ones are sometimes good for Internet Branding . They positively contribute to recall value. However, shorter domains have propensity to lose their traffic to their non hyphenated ones. I call these domains Unfortunate. They don't gain from any spill overs but what they get bleed out to others. You may book both, but don't rely on hyphenated ones solely.
Singular or Plural
One question which is difficult to answer is plural vs. singular. One lose traffic to another. Better have both. However, I prefer singulars, because they are shorter. Though plurals, sometimes, generate more traffic, because of High Recall Value. Apply discretion here according to the situation.
Should You Book Many Domain names?
Lastly, don't try to book too many domain names. Yet again a poor strategy. A domain not in use is worthless. you would find many up for sales, with few takers. Check how many features in expired category! They will tell you the story.