Making learning relevant can be a difficult practice, as what is relevant to one student may not be relevant to another! However, sometimes just connecting the students' learning to what's going on in the world around them can help build the relevance of a certain skill or concept.
For example, when teaching students about government, involve your own city and state governments as part of the instruction. What decisions have been made by the local and/or state government that has impacted the students in your classroom? In our last study of government, our city government had decided to shut down a local swimming pool (which happened to be in one of the lower socioeconomic parts of town...a whole separate topic of discussion) and replace it with a splash pad. The students had no idea that their government made this decision, one which many of them were not happy about. Through this one vehicle, the students experienced how government officials are elected (They were curious just WHO made that decision), the process in making decisions (and of course laws) in the government office, how members of a democratic society can express their views/opinions on issues, including how to respectfully disagree with a decision made by government officials. I assure you, they were more interested in our study of government because of this one "hook" than they would have been had I been standing there telling them facts about government with no connection for them.
A colleague of mine also used a current election of city government officials to drive her study of government, which turned into an amazing unit! The kids even had candidates come in to talk to them so they could make an informed decision on who they wanted to run their local government!
Making learning relevant also has a direct connection to research . When students can decide to learn about topics that are important to them, their learning is automatically made more relevant!
If we stop and take the time to think about ways we can connect students' learning to things that are important to them, the students are going to be more actively involved in their learning, which will result in increased achievement.