1.Install Sketch Preview
Download & install the latest Sketch Preview.plugin (or search in Sketch Toolbox.app) for your Sketch.
Download the Skala Preview.app for Android and Skala Preview.app for Mac OS X, both install.
2.Preview your Sketch files
Open Skala Preview.app on both Android device and Mac. For the first time, the Skala Preview on your Mac will ask for connection, allow.
Open your Sketch file, select an Artboard, then press ⌘ P (or Menu > Plugins > Preview).
Press the “iMac icon” on the nav of Sketch Preview.app in your Android device, choose your Mac’s name in the dialogue window, then you will see your design work on the Android device.
Notice, Sketch > Menubar > Plugins > Preview Setup > Scale to explicit size, you can choose the right size (0.5x/1x/2x/3x/4x) for your Android device’s display.