Watch the Major Scale: Key of D online guitar lesson by Marcy Marxer from Mandolin for Guitar Players
Start on the open D string. Play a full major scale with intervals 1 through 8. Notice that the pattern is the same on both the 3rd and 2nd string. The open 1st string is an E note. E is the 2nd note of the D scale so the pattern will change but the half step will still be between the 3rd and 4th scale tones.