Just started my first week.

Should I do "warm up exercises" from Lesson 2/3 everyday before learning a new technique to practice, such as MUM on day 4?

Or should I just focus on the learning for Day 4, (and everyday thereafter), without doing the "warm up" exercises from lesson 2/3?

We recommend the short day 2 warmup before each new lesson, since each day covers a specific (new) skill and it's ideal that you're warmed up before diving into that skill!

Here's an article with more advice on using the course: https://www.30daysinger.com/blog/one-lesson-per-day-how-to-practice-for-the-best-results.