Test on real devices
If you can, start to build up a "device lab" of older devices (phones/tablets) to view your work on. Having a number of varied devices is hugely beneficial. Not only does it let you feel how a design actually works across different devices, but it also exposes layout/rendering peculiarities earlier in the process. After all, no one enjoys believing that they have finished on a project only to be told it doesn't work properly in a certain environment. Test early, and test often! Buying extra devices need not cost the earth. For example, you can pick up older phone and tablet models on eBay, or buy them from friends/relatives as they upgrade.
Use tools like BrowserSync to synchronize your work
One of the biggest time-saving tools to incorporate into your workflow is BrowserSync. Once configured, as you save your work, any changes to things like CSS are injected into the browser without you needing to refresh your screen constantly...
