Master the scale of C Major first, since this scale has no sharps or flats, and it is easy for the untrained ear to tell if an error is made. Black keys on the piano are separated by white keys, and in patterns of two blacks then three blacks. Find the note "C" by playing the white key to the left of the first of the five black keys. The scale will have eight tones starting with a lower "C" and ending with a higher one. Play all white keys on a keyboard for the "C" scale. Practice the eight notes by starting with the low "C" and ending with a higher one using all of your fingers to play the keys.
Master the scale of C Major first, since this is in the middle of the fretboard, and because the "C" can be identified on most guitars with a dot on the side of the fretboard. Starting with your index finger on the lowest string, play the note on the eighth fret (that's "C"). Without moving your hand, play the note of the next fret up with your middle finger. Staying on the same string, skip a fret and play the note on the 11th fret with your pinkie. Moving your hand over to the next string play the eighth fret note with your index finger, the sixth fret with your middle finger, and the 11th again with your pinkie. Move over one more string (to the third from the bottom) and play the note at the eighth fret with your index finger and the note on the ninth fret with your middle finger. That's a complete scale. Retrace your steps and start over again.
Learn each natural note (no sharps or flats). Play the lowest "C" that you can, and then follow with the notes D, E, F, G, A, B, and end with a higher C. You have played the C Major scale. Go back down the scale starting with your higher C, and then play B, A, G, F, E, D, and end with the low C. Repeat until smooth.