On this video tutorial Aaron Nace from Phlearn looks at how to create a repeatable pattern in Adobe Photoshop.
Although a repeatable pattern is something that is mostly used by graphic designers, it can also be useful in some cases for photographers/retouchers for backgrounds.
The idea in this video is to show users how they can create a repeatable pattern which integrates seamlessly. The problem usually is that after you define a pattern and start using it you can see that it looks like a pattern and you see the repetition. To avoid this you will need to address some issues – in the pattern Nace used you will need to fix the brightness which seems to be uneven on both sides of the pattern sample.
If you want to do something more basic with your background – check out this video by Terry White, on How to Extend Your Background in Adobe Photoshop.