While editing a message, long-press the mic key and select Google Keyboard Settings from the menu that appears. Scroll down the following menu screen until you reach the section titled Gesture Typing. Begin by tapping the ‘Enable gesture typing’ checkbox. Enabling that makes three further options available. ‘Dynamic floating preview’ lets the keyboard show real-time predictions.
‘Show gesture trail’ shows a line of where your finger has been. ‘Phrase gesture’ allows you to include the space bar in your gestures to input multiple words at once. Having set your desired options, press the Back button to return to the message editor. Now, enter text by drawing lines from letter to letter of the word you wish to type; eg T to H to E.