The first, fourth, and fifth chords in a major key have some easy-to-remember diatonic (same key) substitutions that almost always sound great. When we're playing major key popular music, try these:
1 - Instead of Major, try 2, add9, sus, or add4
4 - Instead of Major, try 2, or add9
5 - Instead of Major, try sus, or add4
Simple, but powerful. Quickly knowing what notes to add, and what notes not to add (for example, not playing 4sus because it adds a note that is not diatonic) makes your playing sound more sophisticated.
For example, in the key of G Major:
Instead of G Major, C Major, and D Major
Try G2, Cadd9, and Dsus
In the key of D Major:
Instead of D Major, G Major, and A Major
Try D2, G2, and Asus
Let's try some more interesting chord shapes, in the key of F Major:
Instead of F Major, Bb Major, and C Major:
Try Fadd9, Bb2/F, and Cadd4
You may notice that Bb2/F is the same as an Fsus shape. They contain the same notes: F Bb C. This is called an enharmonic spelling. You can think about this chord as an Fsus, but in relation to how it is played over the fourth chord in the key of F, Bb, it makes more sense to think of it as Bb2/F.