With the root, the perfect fifth and the major third, you lay down the foundation for everything that follows. Whenever you lose your way, you can always go back to these notes to find your footing again. This is why you should only proceed after you have thoroughly mastered them.
The next note is the major second. You will notice that it is slightly more elusive than the notes before. Instead of giving a firm grounding, it will have a more suspended feeling. You may have the tendency to lower the note until you reach the root or to raise the note until you reach the minor or major third. Resist the urge and learn to hold the tension.
If you are having difficulties finding or holding the major second in separation, you can sing simple melodies at a moderate pace. When you reach the major second after a few repetitions, try to hold that note. For example:
do re mi re do re mi re do re mi re (hold)
do re mi re do re mi re do re (hold)
After getting a good grasp of the new note in separation, start jumping between the notes you learned so far. Improvise a bit. It doesn’t have to be fast, it doesn’t have to be beautiful. Don’t think too much. Just do it.