First, learn the solfege forward and backward.

Practice these solfege exercises in order. This will help you learn the syllables forward and backward. Sing them while looking at the image, then try without looking at the image. Then sing while looking at the notes on the staff below.
EXERCISE 1

EXERCISE 1 on the staff

EXERCISE 2

EXERCISE 2 on the staff

Exercise 3

Exercise 4

Listen to Intervals