As discussed, everyday new images are produced for ubuntu for all supported architecture types. I would encourage you to follow along and watch the progression of the OS through these images and your testing. Every data point matters and testing on a regular basis is helpful. So how to get started?
|Settle in with a nice cup of tea while testing!|
For the desktop images everything you need is on the image tracker. There is a wonderful video and text tutorial for helping you get started. You report your results on the tracker itself in a simple web form, so you'll need a launchpad account if you don't have one.
The secondary way to help keep the desktop images in good shape is to install and run the development version of ubuntu on your machine. Each day you can check for updates and update your machine to stay in sync. Use your pc as you normally would, and when you find a bug, report it! Bugs found before the release are much easier to fix than after release.
Now for the phablet images you will need a device capable of running the image. Check out the list. Grab your device and go through the installation process as described on the wiki. Make sure to select the '-proposed' channel when you install so you will see updates to get the latest images being worked on every time they are built. From there you can update everyday. Use the device and when you find a bug, report it! Here's a wiki page to help guide your testing and help you understand how and where to report bugs.
Don't forget there's a whole team of people within ubuntu dedicated to testing just like you. And they would love to have you join them!