Research is an iterative process. No matter how your first set of searching went, there's more to do!
If your search yielded nothing relevant, revisit your keywords and make adjustments. Try new combinations.
If you have too many results but they aren't relevant, add some keywords to narrow down your search.
If you have too few results, try making some of your terms broader, eliminating a term, or adding synonyms.
Even if you found a good article, you aren't done. For many assignments, you'll need more than one article, but not matter how many your assignment requires, it is best to approach research by the rule of 3: For each source required for inclusion in your final assignment you should have skimmed 3. For each you skimmed, you should have done a preliminary evaluation for 3 more. This will help ensure that the 1 that you use in your assignment is the best one available.
Read the titles and abstracts, look at the introductions. Decide which are most promising.
Read the whole article, or at least read the introduction and conclusion thoroughly and skim (proper skimming--not just casting your eyes across the page) the body.
Now not only do you have 1 article that is the best fit, you can articulate why because you've read the alternatives.