The same as if you were targeting a less competitive search term - but more! You could always find a less competitive term... Or use PPC... Or market using a different medium...
If you need to ask then to be honest you are really biting off way more than you can chew. To rank well for a term that gets 68 million searches a day you need to either spend loads and loads of time on site development and link building (I'm talking at least months but more likely years). If that isn't an option you can always pay your way to the top, but for a term like that you are talking about spending some serious $$$. My advice, refine your term. Win the small battles first then go for the big fish!
Just becase a term shows a lot of results, does not mean that it's unobtainable. If it's a commonly used work for example, a lot of people would use it on their pages but they may not actually optimise for it.
68 million results doesn't mean mcuh...check the top 30 and see if you can beat them. If the top 30 is jam with huge authority site, good luck...if they are easy to beat, 68 million and 6.8 billion doesn't make any different