Train your ear to recognize intervals and chord qualities by sound. Listen, take your best guess, and build a streak.
Start with the easy set and just a few intervals — the perfect 5th, the octave, and the major 3rd are the easiest to lock in. Many people anchor each interval to a familiar song (a perfect 4th is the start of "Here Comes the Bride"; a perfect 5th is "Twinkle Twinkle"). Do a few minutes daily and add harder intervals as the easy ones become automatic.
Ear training makes every other skill faster — you'll pick out chords from records, know when you're in tune, and solo by feel. Pair it with the Chord Analyzer to see what you're hearing, or the Chord Quiz to test chord shapes.