A nice drawing of Rarity and Opal, displaying their personality well in the simple pose quite nicely and overall has nothing that upsets the overall composition.
The composition however is a bit plain, but quite acceptable, the background as well has little connection to the piece besides a complimentary color and a place for shadows to be placed on.
Rarity's right fore-leg (the raised hoof) appears smaller and shorter than the rest, Rarity's neck is noticeably thin and connecting oddly to the head but could be accidentally overlooked by how her mane is placed, the back of the neck looks best when it lines up with the back of the head, Rarity's snout is placed too high in relation to the eyes as the eyes should be relatively above the snout, her ear and horn is also placed a bit low, Rarity's mane, the side-part that goes by the neck, appears too small compared to the part of the mane at the top of the head, because of that it loses some balance to the composition, her body appears too long for it's width and could be helped by having the hind leg placed closer or by widening the body (vertically in this instance), the cutie mark is inaccurate in it's design, but it's also quite small in relation to the flank as the cutie mark generally takes up a little over half the space provided there,
the shading used on Rarity's mane is gorgeous! It does however stand out because the level of shading/lighting contrast is not as apparently on Rarity's fur, otherwise really good!
With shading/lighting, the placement does not appear to agree with other parts of the drawings. Highlights are placed when a surface is facing the direct light but based on the mane we have 3 positions, top-left, front, and right. Highlights also stand out to look blobbier than the strand-like brushed appearance of the rest of the mane. Although highlight circles are usable, it doesn't work well at noticeable sizes. Since you've also delved into adding shadows, it's better to apply it to the whole drawing instead of only certain areas.
Examples - a shadow from the horn and adding a shadow where the mane blocks the light.
The backdrop shadow would result from a light source below the characters, but based on the overall lighting, it would have been more logical if the shadow was placed at the same height or shorter of the characters.
Comparing next is Opal which you got the relative size and anatomy correct 'though with a few notes here and there - Again, the highlight does not agree with the shadow, the gem's highlights show the light source from top-right but the shadow should then be the opposite, bottom-left. You also added fur-detail to Opal unlike Rarity, it's nice but not particularly accurate on Opal's face. Opal's legs could probably look a tiny bit better without the little curves on the lines indicating her legs.
Overall there's quite a lot of potential as you do recognize quite a bit of drawing techniques such as how you did Rarity's mane/tail! My suggestion is to just analyze anatomy studies and learning to keep things (light/shadow here) consistent so as to help out in the long run before trying anything complex like poses, backgrounds and such. Hope you're alright with the critique, and will love to see ya continue drawing more!
Thank you very much for your critique on my latest image. I pretty much agree with all of this. The mane for example I am still trying to perfect given that I use a tutorial that my friend/teacher gave to me.
Anatomy wise as I was told once before I think my style comes from when I used to draw sonic the hedgehog characters, rounded haha. But of course I'll study the anatomy of the characters.
I thank you again for the detailed critique on this piece. it will also give me something to look back on for future references.