Before you attempt to increase speed in your playing of the major scale, make sure that your left hand is correctly positioned. Each finger should "line up" with the string being played, and should hover a small distance above it until used. Each finger should also be in line with the four frets being used in the scale. Check your hand position with the following photographs.
This hand position will be difficult at first, but is essential if you are to eventually work up to a fast, smooth sound.
Here is an exercise to help you learn the major scale in all keys. Begin by playing the Root 6 (E formation) G major scale both ascending and descending. Then move to the Root 5 (A formation) C major scale. The next step is to move up one fret and repeat the two patterns in the keys of Ab major and Db major. If you keep progressing up the fretboard, it doesn’t take long until you have covered all possible keys. It is a good idea to say the name of each key as you play the scale.