If you were assigned a topic, but the general subject that you were assigned isn't of interest to you, you may find an aspect within the topic that does grab you.
If you are assigned a paper on business ethics, but you are more interested in organizations like the American Red Cross, you might write about ethical questions that are particularly troublesome for managers of non-profit organizations, for example.
How you manage the topic depends considerably on the purpose of the assignment and the level of the class. Certainly, a first-year paper for ENGL 1013 is going to be different in character and purpose from one for a higher-level class in a subject discipline. Check your assignment sheet and ask the instructor for more information, if in doubt.
If you have freedom to choose your topic, write or present about something that is a passion to you-- if it's interesting to you, it will be easier to write or talk about.
However, don't rant. Use something that is not a religious or political subject, a television show, or a hobby, unless there is a way to make it more palatable to the audience, especially if you are making a speech.
For example, writing a paper about how much you like to go deer hunting is probably not the best choice. Writing about the effect that overpopulation has on the health and well-being of the deer and the surrounding ecology might be better. Or, a paper on populations of deer in suburban areas, which are an issue, with the problems and benefits of population control by hunting or some other means, might be of more interest to your audience. In Australia, they have a similar problem with kangaroos.
Use place/geography, time, gender, and other factors to limit a topic.
For example, rather than trying to write a paper about 'poverty,' exploring possible solutions to infant mortality in Afghanistan (which, according to an article in Lancet, has the highest rate of child mortality in the world*)--or comparing the effect of poverty on infants in Afghanistan to the effect of poverty on infants in the United States might be both more compelling and more easily completed than trying to cover the whole subject.
However, keep in mind that information is more easily found about some topics than others-- there is much more information readily available about the United States than about Afghanistan, for example.
* See Loewenberg, S, (2009). Afghanistan's hidden health issue, The Lancet, Volume 374, Issue 9700, 31 October 2009-6 November 2009, Pages 1487-1488, DOI: 10.1016/S0140-6736(09)61887-0.