Comes with practice, so going forward whether solo or working with an instructor just try to explain out loud everything your are doing, why you are doing it, what you are looking for (sight pictures), what you are planning to do (this helps the student learn to think ahead and be ready for what will happen in 30 seconds or 5 minutes).
I am a big fan of recording yourself. Pick up a cheap digital sound recorder and either use a spare headphone jack to input to your recorder (a short 1/4" guitar cable with a 1/4 female to 3.5mm male adapter) or you can pick up a small wired lapel mic and tape it inside your headphone earcup. What you think you say and portray are often very different from reality, so being able to critically assess yourself is really helpful in approving. The first few times you might think you sound really dumb and bumbly.. that's ok, that's the whole point of assessing and learning.
First just work on talking things through, especially the "why I'm doing what I'm doing" part. Then as that becomes more natural, start to work on brevity. Less is often more in a busy and stressful learning environment like a student pilot in the cockpit.