It doesn't take much time to do favours that help you build better professional and personal relationships. Sometimes, even things that only take a few minutes can make a big difference to someone.
For example, if someone tells you about an issue they're having with formatting their email, you could send them an article or Q&A that addresses their issue. I've taken a few minutes out of my day to search for restaurant recommendations for friends or family visiting the city I live in. You show that you were listening to their problem and try to help them without diverting too much of your own time.
As Aja Frost points out, you can also be proactive about your five minute favours:
When the web team unveils the new site, you can take five minutes to send them your thoughts. When you notice two colleagues have mutual interests (because you're paying attention!), you can offer to introduce them. When someone you know announces a new side project, you can promote it on social media.
This doesn't mean you need to spend all day doing favours for everyone else -- but if you can spare a few moments, you can build a lot of goodwill.