There are several challenges you face when trying to evaluate the traffic to your site.
You 1st need to evaluate the source: What analytics program are you using, how does it collect data, what are ways that data can be corrupted or skewed?
You then need to establish reporting: What frequency will you evaluate; hourly, daily, weekly, monthly, yearly, or all of the above? Do you understand the metrics of the reports? Do you need hard #'s, percentages, or both? What about charts, everyone loves charts!?!
Once your done playing Devil's Advocate and have your reports in hand, now comes the real work- Analyze the data. This is where many will throw their compass in the water and try and steer by the stars. This is also the point where I tell you that most people are not objective in their review of data, specifically when they have a direct interest in the data they are reviewing. The best advice I can give is: Be aware that you are biased and hopefully you can try and take a more objective stance when analyzing future data. I often recommend getting trusted, intelligent individuals who have no stake in the information to review and give you their quick opinion on the data, it can really open your eyes. In most cases it will show you obvious big picture information that may have been overlooked, or it can simply confirm your evaluation of the situation.
Many have heard of "Analysis Paralysis" and many others have experienced this malady. The best way to avoid analytic confusion is to keep the big picture in mind (Key Performance Indexes), understand the metrics, and ALWAYS compare apples to apples when possible.