AS mona_klixxx correctly pointed out, SEO is a long term strategy. Change your meta's and it could take 2 weeks for them to propagate through Google and if they are still not right, this could take months of tweaking in itself.
SEM is the best tactic to get traffic quickly but can be expensive if your keyword selection, placement positioning and advertising messages don't appeal to the right sort of customer. However if your get your proposition right, you will be rewarded with traffic and the next challenge would be to convert guests into members. Neither SEO or SEM can provide you with that.
Good Luck
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