The basic steps to checking facts involve finding the source, establishing the source's authority in the matter and considering what variables affect perceptions about the issue, reports CUNY. Finding such information involves speaking with primary sources when possible and using periodicals and other secondary resources as needed.
After talking to primary sources, PolitiFact.com suggests looking for research on the issue already done by others. See what these sources turn up, and verify their conclusions independently. PolitiFact also recommends elaborate Google searches using as many combinations of search terms as possible. Use the basic terms, and then try searches on closely related issues.
Use the library to access commercial search sites such as Lexis Nexis and CQ to find information that doesn't show up in Google. Check out books on the issue as often as possible. Talk to experts in related fields to learn more about the topic, and then ask those experts whose opinions they respect in order to find more sources.
Try to look at the issue from as many angles as possible so as not to miss important context. Speak with sources who represent different perspectives. Once the main share of this work is done, step away from it for a little while to think. Sometimes taking a break allows one the perspective to see new information or an angle previously overlooked.