Note any unusual occurrences or observations experienced in collecting your data. It may otherwise be assumed that an experimenter who doesn't reveal his or her raw data has something to hide. Analyze the resulting data so that you can draw conclusions. If the problem was properly stated, the experiment properly designed and carried out, and the data not corrupted by outside factors, the analysis and interpretation ought to be accomplishable. Often the interpretation is relatively easy, sometimes not.
Experiments never fail, but experimenters do.
Discuss negative results. It is dishonest, and bad science, to present only those data supporting your hypothesis. Contrary evidence must be presented and explained. Eventually the truth prevails, and you will not do yourself any favors by misrepresenting the truth. Your negative results could be ultimately more significant and important than simple unequivocal agreement with your hypothesis or the hypothesis of others from the literature.