The Luna and Celestia related drawings I did over the weekend and a bit earlier this week. This should be all the ones I have on tumblr so far.
A lot of it is just practice, especially with the expressions. The top drawings are just some quick mockups to get a feel for proportions compared to one another and then rough layout for design. I also did some rough poses to work with when I do the final drawings for them.
Yeah, that's about it I guess.