Making sure that your project will be successful really boils down to two things: 1) get things done, 2) get feedback.
It’s obvious why getting things done matters: if you want to move forward, you need to get things done. Getting things done is however not a sufficient condition to be successful. You could be moving in the wrong direction! To be successful you need to constantly get feedback and steer the ongoing progress towards the goal.
These two principles are the heart of the agile manifesto: Move one step forward, adjust, and repeat. That’s the best strategy to ensure that what’s produced is really helpful for the project.
A step can be small or big. It can be the implementation of a single method with a peer review as feedback. It can be a refactoring with the automated execution of unit tests as feedback. It can be the implementation of a feature with the customer demo as feedback.
Scrum and XP are very different but are both considered “implementations” of the agile manifesto, since both promote moving forward and getting feedback in their own way.
Scrum is a technology-agnostic process to get things done. The work is split in stories and tasks, which are small actionable items. To keep the momentum high, team members should focus on one task at a time. Feedback is obtained during the daily standup, the sprint review and sprint retrospective. You can use Scrum to conduct any project, not just software development.
XP on the hand is organised around technical software practices. It emphasizes pair programming, unit testing, continuous integration, refactoring, collective code ownership. The first three practices are nothing else than ways to get feedback about the code. Refactoring and collective code ownership are ways to guarantee that the team can always move forward.
With little surprise, XP and Scrum are good complements to each other. But they can also be complemented with other elements of your own. If something works for you to improve getting things done or getting feedback, add it.
Make sure that feedback doesn’t turn into noise though. If feedback is not actionable it’s not truly feedback. What you want is feedback that help you get your next thing done in a better way. That’s the loop.