Firstly, students should identity whether the source is primary or secondary. Primary sources are those that are directly produced from events such as an eyewitness account. Secondary sources are those produced from primary sources such as a newspaper article produced from an eyewitness account.
The type of source should then be used to determine its validity in accessing a historical question or creating a narrative, for example. For students at GCSE level this will involve accessing the usefulness of the source.
The validity and type of source are often determined by its provenance. Students should ask whether the reasons the source was created and where the source is from affect its usefulness and reliability to provide an accurate historical insight. For example, a propaganda piece is less useful than an eyewitness account. However, both reveal certain historical features that are useful and both are biased and thus limited in some way.
Finally, students should access when the source was created to determine its usefulness in studying a particular period of history. For example, a government record from the reign of James I & VI of England and Scotland is more useful for studying the Stuart dynasty than a Roman eyewitness account of the siege of Rome in 410 A.D.